diff --git a/Signal/src/Models/PhoneNumberValidator.swift b/Signal/src/Models/PhoneNumberValidator.swift
index dcab1e017..4adf74387 100644
--- a/Signal/src/Models/PhoneNumberValidator.swift
+++ b/Signal/src/Models/PhoneNumberValidator.swift
@@ -35,19 +35,13 @@ public class PhoneNumberValidator: NSObject {
 
     let validBrazilPhoneNumberRegex = try! NSRegularExpression(pattern: "^\\+55\\d{2}9?\\d{8}$", options: [])
     private func isValidForBrazilRegistration(phoneNumber: PhoneNumber) -> Bool {
-        guard let e164 = phoneNumber.toE164() else {
-            return false
-        }
-
+        let e164 = phoneNumber.toE164()
         return validBrazilPhoneNumberRegex.hasMatch(input: e164)
     }
 
     let validUnitedStatesPhoneNumberRegex = try! NSRegularExpression(pattern: "^\\+1\\d{10}$", options: [])
     private func isValidForUnitedStatesRegistration(phoneNumber: PhoneNumber) -> Bool {
-        guard let e164 = phoneNumber.toE164() else {
-            return false
-        }
-
+        let e164 = phoneNumber.toE164()
         return validUnitedStatesPhoneNumberRegex.hasMatch(input: e164)
     }
 }
diff --git a/SignalServiceKit/src/Account/TSPreKeyManager.h b/SignalServiceKit/src/Account/TSPreKeyManager.h
index 7295c20ee..4f9253f71 100644
--- a/SignalServiceKit/src/Account/TSPreKeyManager.h
+++ b/SignalServiceKit/src/Account/TSPreKeyManager.h
@@ -1,9 +1,11 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "TSAccountManager.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface TSPreKeyManager : NSObject
 
 #pragma mark - State Tracking
@@ -30,3 +32,5 @@
 + (void)checkPreKeysIfNecessary;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Contacts/PhoneNumber.h b/SignalServiceKit/src/Contacts/PhoneNumber.h
index b83ce28a0..8418a5c69 100644
--- a/SignalServiceKit/src/Contacts/PhoneNumber.h
+++ b/SignalServiceKit/src/Contacts/PhoneNumber.h
@@ -1,7 +1,9 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
+NS_ASSUME_NONNULL_BEGIN
+
 #define COUNTRY_CODE_PREFIX @"+"
 
 /**
@@ -12,10 +14,10 @@
  */
 @interface PhoneNumber : NSObject
 
-+ (PhoneNumber *)phoneNumberFromE164:(NSString *)text;
++ (nullable PhoneNumber *)phoneNumberFromE164:(NSString *)text;
 
-+ (PhoneNumber *)tryParsePhoneNumberFromUserSpecifiedText:(NSString *)text;
-+ (PhoneNumber *)tryParsePhoneNumberFromE164:(NSString *)text;
++ (nullable PhoneNumber *)tryParsePhoneNumberFromUserSpecifiedText:(NSString *)text;
++ (nullable PhoneNumber *)tryParsePhoneNumberFromE164:(NSString *)text;
 
 // This will try to parse the input text as a phone number using
 // the default region and the country code for this client's phone
@@ -35,7 +37,7 @@
 
 - (NSURL *)toSystemDialerURL;
 - (NSString *)toE164;
-- (NSNumber *)getCountryCode;
+- (nullable NSNumber *)getCountryCode;
 @property (nonatomic, readonly, nullable) NSString *nationalNumber;
 - (BOOL)isValid;
 
@@ -44,3 +46,5 @@
 + (NSString *)defaultCountryCode;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Contacts/PhoneNumber.m b/SignalServiceKit/src/Contacts/PhoneNumber.m
index 064c0f81c..b234f6c97 100644
--- a/SignalServiceKit/src/Contacts/PhoneNumber.m
+++ b/SignalServiceKit/src/Contacts/PhoneNumber.m
@@ -10,6 +10,8 @@
 #import <libPhoneNumber_iOS/NBPhoneNumber.h>
 #import <libPhoneNumber_iOS/NBPhoneNumberUtil.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 static NSString *const RPDefaultsKeyPhoneNumberString    = @"RPDefaultsKeyPhoneNumberString";
 static NSString *const RPDefaultsKeyPhoneNumberCanonical = @"RPDefaultsKeyPhoneNumberCanonical";
 
@@ -36,7 +38,7 @@ static NSString *const RPDefaultsKeyPhoneNumberCanonical = @"RPDefaultsKeyPhoneN
     return self;
 }
 
-+ (PhoneNumber *)phoneNumberFromText:(NSString *)text andRegion:(NSString *)regionCode {
++ (nullable PhoneNumber *)phoneNumberFromText:(NSString *)text andRegion:(NSString *)regionCode {
     OWSAssertDebug(text != nil);
     OWSAssertDebug(regionCode != nil);
 
@@ -59,7 +61,7 @@ static NSString *const RPDefaultsKeyPhoneNumberCanonical = @"RPDefaultsKeyPhoneN
     return [[PhoneNumber alloc] initWithPhoneNumber:number e164:e164];
 }
 
-+ (PhoneNumber *)phoneNumberFromUserSpecifiedText:(NSString *)text {
++ (nullable PhoneNumber *)phoneNumberFromUserSpecifiedText:(NSString *)text {
     OWSAssertDebug(text != nil);
 
     return [PhoneNumber phoneNumberFromText:text andRegion:[self defaultCountryCode]];
@@ -86,7 +88,7 @@ static NSString *const RPDefaultsKeyPhoneNumberCanonical = @"RPDefaultsKeyPhoneN
     return countryCode;
 }
 
-+ (PhoneNumber *)phoneNumberFromE164:(NSString *)text {
++ (nullable PhoneNumber *)phoneNumberFromE164:(NSString *)text {
     OWSAssertDebug(text != nil);
     OWSAssertDebug([text hasPrefix:COUNTRY_CODE_PREFIX]);
     PhoneNumber *number = [PhoneNumber phoneNumberFromText:text andRegion:@"ZZ"];
@@ -170,7 +172,7 @@ static NSString *const RPDefaultsKeyPhoneNumberCanonical = @"RPDefaultsKeyPhoneN
     return regionCode;
 }
 
-+ (PhoneNumber *)tryParsePhoneNumberFromUserSpecifiedText:(NSString *)text {
++ (nullable PhoneNumber *)tryParsePhoneNumberFromUserSpecifiedText:(NSString *)text {
     OWSAssertDebug(text != nil);
 
     if ([text isEqualToString:@""]) {
@@ -181,7 +183,7 @@ static NSString *const RPDefaultsKeyPhoneNumberCanonical = @"RPDefaultsKeyPhoneN
     return [self phoneNumberFromUserSpecifiedText:sanitizedString];
 }
 
-+ (NSString *)nationalPrefixTransformRuleForDefaultRegion
++ (nullable NSString *)nationalPrefixTransformRuleForDefaultRegion
 {
     static NSString *result = nil;
     static dispatch_once_t onceToken;
@@ -195,7 +197,7 @@ static NSString *const RPDefaultsKeyPhoneNumberCanonical = @"RPDefaultsKeyPhoneN
 }
 
 // clientPhoneNumber is the local user's phone number and should never change.
-+ (NSString *)nationalPrefixTransformRuleForClientPhoneNumber:(NSString *)clientPhoneNumber
++ (nullable NSString *)nationalPrefixTransformRuleForClientPhoneNumber:(NSString *)clientPhoneNumber
 {
     if (clientPhoneNumber.length < 1) {
         return nil;
@@ -499,7 +501,7 @@ static NSString *const RPDefaultsKeyPhoneNumberCanonical = @"RPDefaultsKeyPhoneN
     return [NSString stringWithUTF8String:(void *)outputString];
 }
 
-+ (PhoneNumber *)tryParsePhoneNumberFromE164:(NSString *)text {
++ (nullable PhoneNumber *)tryParsePhoneNumberFromE164:(NSString *)text {
     OWSAssertDebug(text != nil);
     if (![text hasPrefix:COUNTRY_CODE_PREFIX]) {
         return nil;
@@ -517,7 +519,7 @@ static NSString *const RPDefaultsKeyPhoneNumberCanonical = @"RPDefaultsKeyPhoneN
     return self.e164;
 }
 
-- (NSNumber *)getCountryCode {
+- (nullable NSNumber *)getCountryCode {
     return self.phoneNumber.countryCode;
 }
 
@@ -573,3 +575,5 @@ static NSString *const RPDefaultsKeyPhoneNumberCanonical = @"RPDefaultsKeyPhoneN
 }
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Contacts/PhoneNumberUtil.h b/SignalServiceKit/src/Contacts/PhoneNumberUtil.h
index b6ecd5050..416d893b1 100644
--- a/SignalServiceKit/src/Contacts/PhoneNumberUtil.h
+++ b/SignalServiceKit/src/Contacts/PhoneNumberUtil.h
@@ -1,10 +1,12 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "PhoneNumber.h"
 #import <libPhoneNumber_iOS/NBPhoneNumberUtil.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface PhoneNumberUtil : NSObject
 
 @property (nonatomic, retain) NBPhoneNumberUtil *nbPhoneNumberUtil;
@@ -17,7 +19,7 @@
 
 + (NSString *)callingCodeFromCountryCode:(NSString *)countryCode;
 + (NSString *)countryNameFromCountryCode:(NSString *)countryCode;
-+ (NSArray *)countryCodesForSearchTerm:(NSString *)searchTerm;
++ (NSArray *)countryCodesForSearchTerm:(nullable NSString *)searchTerm;
 
 // Returns a list of country codes for a calling code in descending
 // order of population.
@@ -32,9 +34,11 @@
 
 + (NSString *)examplePhoneNumberForCountryCode:(NSString *)countryCode;
 
-- (NBPhoneNumber *)parse:(NSString *)numberToParse defaultRegion:(NSString *)defaultRegion error:(NSError **)error;
+- (nullable NBPhoneNumber *)parse:(NSString *)numberToParse defaultRegion:(NSString *)defaultRegion error:(NSError **)error;
 - (NSString *)format:(NBPhoneNumber *)phoneNumber
         numberFormat:(NBEPhoneNumberFormat)numberFormat
                error:(NSError **)error;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Contacts/PhoneNumberUtil.m b/SignalServiceKit/src/Contacts/PhoneNumberUtil.m
index c2e80093b..359f0a9ab 100644
--- a/SignalServiceKit/src/Contacts/PhoneNumberUtil.m
+++ b/SignalServiceKit/src/Contacts/PhoneNumberUtil.m
@@ -1,5 +1,5 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "PhoneNumberUtil.h"
@@ -7,6 +7,8 @@
 #import "FunctionalUtil.h"
 #import <libPhoneNumber_iOS/NBPhoneNumber.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface PhoneNumberUtil ()
 
 @property (nonatomic, readonly) NSMutableDictionary *countryCodesFromCallingCodeCache;
@@ -467,7 +469,7 @@
 }
 
 // search term -> country codes
-+ (NSArray *)countryCodesForSearchTerm:(NSString *)searchTerm {
++ (NSArray *)countryCodesForSearchTerm:(nullable NSString *)searchTerm {
     searchTerm = [searchTerm stringByTrimmingCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
 
     NSArray *countryCodes = NSLocale.ISOCountryCodes;
@@ -602,3 +604,5 @@
 }
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Contacts/TSThread.m b/SignalServiceKit/src/Contacts/TSThread.m
index 97e95158d..a3cbfb5f4 100644
--- a/SignalServiceKit/src/Contacts/TSThread.m
+++ b/SignalServiceKit/src/Contacts/TSThread.m
@@ -46,7 +46,7 @@ ConversationColorName const kConversationColorName_Default = ConversationColorNa
 
 @property (nonatomic) NSDate *creationDate;
 @property (nonatomic) NSString *conversationColorName;
-@property (nonatomic) NSNumber *archivedAsOfMessageSortId;
+@property (nonatomic, nullable) NSNumber *archivedAsOfMessageSortId;
 @property (nonatomic, copy, nullable) NSString *messageDraft;
 @property (atomic, nullable) NSDate *mutedUntilDate;
 
diff --git a/SignalServiceKit/src/Messages/OWSMessageServiceParams.h b/SignalServiceKit/src/Messages/OWSMessageServiceParams.h
index 99f719097..a2e1d9d3f 100644
--- a/SignalServiceKit/src/Messages/OWSMessageServiceParams.h
+++ b/SignalServiceKit/src/Messages/OWSMessageServiceParams.h
@@ -1,10 +1,12 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "TSConstants.h"
 #import <Mantle/Mantle.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 /**
  * Contstructs the per-device-message parameters used when submitting a message to
  * the Signal Web Service.
@@ -31,3 +33,5 @@
               registrationId:(int)registrationId;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Messages/OWSMessageServiceParams.m b/SignalServiceKit/src/Messages/OWSMessageServiceParams.m
index 8cd539dea..a2a66121c 100644
--- a/SignalServiceKit/src/Messages/OWSMessageServiceParams.m
+++ b/SignalServiceKit/src/Messages/OWSMessageServiceParams.m
@@ -1,11 +1,13 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "OWSMessageServiceParams.h"
 #import "TSConstants.h"
 #import <SignalCoreKit/NSData+OWS.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 @implementation OWSMessageServiceParams
 
 + (NSDictionary *)JSONKeyPathsByPropertyKey
@@ -39,3 +41,5 @@
 }
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Messages/OWSReadTracking.h b/SignalServiceKit/src/Messages/OWSReadTracking.h
index e3314ea83..d135837e5 100644
--- a/SignalServiceKit/src/Messages/OWSReadTracking.h
+++ b/SignalServiceKit/src/Messages/OWSReadTracking.h
@@ -1,7 +1,9 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
+NS_ASSUME_NONNULL_BEGIN
+
 @class YapDatabaseReadWriteTransaction;
 
 /**
@@ -30,3 +32,5 @@
                   transaction:(YapDatabaseReadWriteTransaction *)transaction;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Network/API/Requests/TSRequest.h b/SignalServiceKit/src/Network/API/Requests/TSRequest.h
index 069a706d0..25e9c3933 100644
--- a/SignalServiceKit/src/Network/API/Requests/TSRequest.h
+++ b/SignalServiceKit/src/Network/API/Requests/TSRequest.h
@@ -1,7 +1,9 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
+NS_ASSUME_NONNULL_BEGIN
+
 @class SMKUDAccessKey;
 
 @interface TSRequest : NSMutableURLRequest
@@ -30,3 +32,5 @@
                     parameters:(nullable NSDictionary<NSString *, id> *)parameters;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Network/API/Requests/TSRequest.m b/SignalServiceKit/src/Network/API/Requests/TSRequest.m
index e253706f7..c36c861da 100644
--- a/SignalServiceKit/src/Network/API/Requests/TSRequest.m
+++ b/SignalServiceKit/src/Network/API/Requests/TSRequest.m
@@ -1,5 +1,5 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "TSRequest.h"
@@ -8,6 +8,8 @@
 #import <SignalCoreKit/NSData+OWS.h>
 #import <SignalMetadataKit/SignalMetadataKit-Swift.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 @implementation TSRequest
 
 @synthesize authUsername = _authUsername;
@@ -94,7 +96,7 @@
     }
 }
 
-- (NSString *)authUsername
+- (nullable NSString *)authUsername
 {
     OWSAssertDebug(self.shouldHaveAuthorizationHeaders);
 
@@ -103,7 +105,7 @@
     }
 }
 
-- (NSString *)authPassword
+- (nullable NSString *)authPassword
 {
     OWSAssertDebug(self.shouldHaveAuthorizationHeaders);
 
@@ -113,3 +115,5 @@
 }
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Network/API/TSNetworkManager.m b/SignalServiceKit/src/Network/API/TSNetworkManager.m
index 660f478d1..ae05d6e8f 100644
--- a/SignalServiceKit/src/Network/API/TSNetworkManager.m
+++ b/SignalServiceKit/src/Network/API/TSNetworkManager.m
@@ -15,6 +15,8 @@
 #import <SignalCoreKit/NSData+OWS.h>
 #import <SignalServiceKit/SignalServiceKit-Swift.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 NSErrorDomain const TSNetworkManagerErrorDomain = @"SignalServiceKit.TSNetworkManager";
 
 BOOL IsNSErrorNetworkFailure(NSError *_Nullable error)
@@ -427,9 +429,9 @@ typedef void (^failureBlock)(NSURLSessionDataTask *task, NSError *error);
 }
 
 + (NSError *)errorWithHTTPCode:(NSInteger)code
-                   description:(NSString *)description
-                 failureReason:(NSString *)failureReason
-            recoverySuggestion:(NSString *)recoverySuggestion
+                   description:(nullable NSString *)description
+                 failureReason:(nullable NSString *)failureReason
+            recoverySuggestion:(nullable NSString *)recoverySuggestion
                  fallbackError:(NSError *)fallbackError
 {
     OWSAssertDebug(fallbackError);
@@ -468,3 +470,5 @@ typedef void (^failureBlock)(NSURLSessionDataTask *task, NSError *error);
 }
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Storage/AxolotlStore/OWSPrimaryStorage+PreKeyStore.h b/SignalServiceKit/src/Storage/AxolotlStore/OWSPrimaryStorage+PreKeyStore.h
index 40f0f0c92..286c388e8 100644
--- a/SignalServiceKit/src/Storage/AxolotlStore/OWSPrimaryStorage+PreKeyStore.h
+++ b/SignalServiceKit/src/Storage/AxolotlStore/OWSPrimaryStorage+PreKeyStore.h
@@ -1,13 +1,17 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "OWSPrimaryStorage.h"
 #import <AxolotlKit/PreKeyStore.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface OWSPrimaryStorage (PreKeyStore) <PreKeyStore>
 
 - (NSArray<PreKeyRecord *> *)generatePreKeyRecords;
 - (void)storePreKeyRecords:(NSArray<PreKeyRecord *> *)preKeyRecords NS_SWIFT_NAME(storePreKeyRecords(_:));
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Storage/AxolotlStore/OWSPrimaryStorage+PreKeyStore.m b/SignalServiceKit/src/Storage/AxolotlStore/OWSPrimaryStorage+PreKeyStore.m
index 5035b4383..015bdb252 100644
--- a/SignalServiceKit/src/Storage/AxolotlStore/OWSPrimaryStorage+PreKeyStore.m
+++ b/SignalServiceKit/src/Storage/AxolotlStore/OWSPrimaryStorage+PreKeyStore.m
@@ -1,5 +1,5 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "OWSPrimaryStorage+PreKeyStore.h"
@@ -14,6 +14,8 @@
 #define TSNextPrekeyIdKey @"TSStorageInternalSettingsNextPreKeyId"
 #define BATCH_SIZE 100
 
+NS_ASSUME_NONNULL_BEGIN
+
 @implementation OWSPrimaryStorage (PreKeyStore)
 
 - (NSArray<PreKeyRecord *> *)generatePreKeyRecords;
@@ -100,3 +102,5 @@
 }
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Storage/AxolotlStore/OWSPrimaryStorage+keyFromIntLong.h b/SignalServiceKit/src/Storage/AxolotlStore/OWSPrimaryStorage+keyFromIntLong.h
index b7e70c632..d081148c1 100644
--- a/SignalServiceKit/src/Storage/AxolotlStore/OWSPrimaryStorage+keyFromIntLong.h
+++ b/SignalServiceKit/src/Storage/AxolotlStore/OWSPrimaryStorage+keyFromIntLong.h
@@ -1,11 +1,15 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "OWSPrimaryStorage.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface OWSPrimaryStorage (keyFromIntLong)
 
 - (NSString *)keyFromInt:(int)integer;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Storage/AxolotlStore/OWSPrimaryStorage+keyFromIntLong.m b/SignalServiceKit/src/Storage/AxolotlStore/OWSPrimaryStorage+keyFromIntLong.m
index 8c41ccac1..428897fd5 100644
--- a/SignalServiceKit/src/Storage/AxolotlStore/OWSPrimaryStorage+keyFromIntLong.m
+++ b/SignalServiceKit/src/Storage/AxolotlStore/OWSPrimaryStorage+keyFromIntLong.m
@@ -1,9 +1,11 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "OWSPrimaryStorage+keyFromIntLong.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @implementation OWSPrimaryStorage (keyFromIntLong)
 
 - (NSString *)keyFromInt:(int)integer
@@ -12,3 +14,5 @@
 }
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Storage/SSKMessageSenderJobRecord.m b/SignalServiceKit/src/Storage/SSKMessageSenderJobRecord.m
index c54357c02..d7d92a480 100644
--- a/SignalServiceKit/src/Storage/SSKMessageSenderJobRecord.m
+++ b/SignalServiceKit/src/Storage/SSKMessageSenderJobRecord.m
@@ -1,10 +1,12 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "SSKMessageSenderJobRecord.h"
 #import "TSOutgoingMessage.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @implementation SSKMessageSenderJobRecord
 
 #pragma mark
@@ -45,3 +47,5 @@
 }
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Storage/TSDatabaseSecondaryIndexes.h b/SignalServiceKit/src/Storage/TSDatabaseSecondaryIndexes.h
index 81cab7d1b..f2e377654 100644
--- a/SignalServiceKit/src/Storage/TSDatabaseSecondaryIndexes.h
+++ b/SignalServiceKit/src/Storage/TSDatabaseSecondaryIndexes.h
@@ -1,10 +1,12 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import <YapDatabase/YapDatabaseSecondaryIndex.h>
 #import <YapDatabase/YapDatabaseTransaction.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface TSDatabaseSecondaryIndexes : NSObject
 
 + (NSString *)registerTimeStampIndexExtensionName;
@@ -16,3 +18,5 @@
                       usingTransaction:(YapDatabaseReadTransaction *)transaction;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Storage/TSDatabaseSecondaryIndexes.m b/SignalServiceKit/src/Storage/TSDatabaseSecondaryIndexes.m
index b0e0f46d0..d31c677d9 100644
--- a/SignalServiceKit/src/Storage/TSDatabaseSecondaryIndexes.m
+++ b/SignalServiceKit/src/Storage/TSDatabaseSecondaryIndexes.m
@@ -1,11 +1,13 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "TSDatabaseSecondaryIndexes.h"
 #import "OWSStorage.h"
 #import "TSInteraction.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 #define TSTimeStampSQLiteIndex @"messagesTimeStamp"
 
 @implementation TSDatabaseSecondaryIndexes
@@ -48,3 +50,5 @@
 }
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Storage/TSDatabaseView.h b/SignalServiceKit/src/Storage/TSDatabaseView.h
index d0e126dc0..65fa2571a 100644
--- a/SignalServiceKit/src/Storage/TSDatabaseView.h
+++ b/SignalServiceKit/src/Storage/TSDatabaseView.h
@@ -1,10 +1,12 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "OWSStorage.h"
 #import <YapDatabase/YapDatabaseViewTransaction.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 extern NSString *const TSInboxGroup;
 extern NSString *const TSArchiveGroup;
 extern NSString *const TSUnreadIncomingMessagesGroup;
@@ -68,3 +70,5 @@ extern NSString *const TSLazyRestoreAttachmentsDatabaseViewExtensionName;
 + (void)asyncRegisterLazyRestoreAttachmentsDatabaseView:(OWSStorage *)storage;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Storage/TSDatabaseView.m b/SignalServiceKit/src/Storage/TSDatabaseView.m
index 0034af82f..a565ceae3 100644
--- a/SignalServiceKit/src/Storage/TSDatabaseView.m
+++ b/SignalServiceKit/src/Storage/TSDatabaseView.m
@@ -15,6 +15,8 @@
 #import <YapDatabase/YapDatabaseCrossProcessNotification.h>
 #import <YapDatabase/YapDatabaseViewTypes.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 NSString *const TSInboxGroup = @"TSInboxGroup";
 NSString *const TSArchiveGroup = @"TSArchiveGroup";
 
@@ -507,3 +509,5 @@ NSString *const TSLazyRestoreAttachmentsGroup = @"TSLazyRestoreAttachmentsGroup"
 }
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Storage/TSStorageKeys.h b/SignalServiceKit/src/Storage/TSStorageKeys.h
index b18a8205f..68068758d 100644
--- a/SignalServiceKit/src/Storage/TSStorageKeys.h
+++ b/SignalServiceKit/src/Storage/TSStorageKeys.h
@@ -1,7 +1,9 @@
 //
-//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
+NS_ASSUME_NONNULL_BEGIN
+
 #ifndef TextSecureKit_TSStorageKeys_h
 #define TextSecureKit_TSStorageKeys_h
 
@@ -24,3 +26,5 @@
 #define TSStorageInternalSettingsVersion @"TSLastLaunchedVersion"
 
 #endif
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/TSConstants.h b/SignalServiceKit/src/TSConstants.h
index 82f58d620..8c327b503 100644
--- a/SignalServiceKit/src/TSConstants.h
+++ b/SignalServiceKit/src/TSConstants.h
@@ -2,6 +2,8 @@
 //  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
+NS_ASSUME_NONNULL_BEGIN
+
 #ifndef TextSecureKit_Constants_h
 #define TextSecureKit_Constants_h
 
@@ -67,3 +69,5 @@ BOOL IsUsingProductionService(void);
 #define SignalApplicationGroup @"group.org.whispersystems.signal.group"
 
 #endif
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/TSConstants.m b/SignalServiceKit/src/TSConstants.m
index b5b92adef..b82b9e0e7 100644
--- a/SignalServiceKit/src/TSConstants.m
+++ b/SignalServiceKit/src/TSConstants.m
@@ -1,9 +1,11 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "TSConstants.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 BOOL IsUsingProductionService()
 {
 #ifdef USING_PRODUCTION_SERVICE
@@ -12,3 +14,5 @@ BOOL IsUsingProductionService()
     return NO;
 #endif
 }
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Util/AppVersion.h b/SignalServiceKit/src/Util/AppVersion.h
index 02699caf5..8c48c0f7e 100755
--- a/SignalServiceKit/src/Util/AppVersion.h
+++ b/SignalServiceKit/src/Util/AppVersion.h
@@ -1,18 +1,20 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface AppVersion : NSObject
 
 // The properties are updated immediately after launch.
 @property (atomic, readonly) NSString *firstAppVersion;
-@property (atomic, readonly) NSString *lastAppVersion;
+@property (atomic, nullable, readonly) NSString *lastAppVersion;
 @property (atomic, readonly) NSString *currentAppVersion;
 
 // There properties aren't updated until appLaunchDidComplete is called.
-@property (atomic, readonly) NSString *lastCompletedLaunchAppVersion;
-@property (atomic, readonly) NSString *lastCompletedLaunchMainAppVersion;
-@property (atomic, readonly) NSString *lastCompletedLaunchSAEAppVersion;
+@property (atomic, nullable, readonly) NSString *lastCompletedLaunchAppVersion;
+@property (atomic, nullable, readonly) NSString *lastCompletedLaunchMainAppVersion;
+@property (atomic, nullable, readonly) NSString *lastCompletedLaunchSAEAppVersion;
 
 - (instancetype)init NS_UNAVAILABLE;
 
@@ -24,3 +26,5 @@
 - (BOOL)isFirstLaunch;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Util/AppVersion.m b/SignalServiceKit/src/Util/AppVersion.m
index 503c60420..4eda544e3 100755
--- a/SignalServiceKit/src/Util/AppVersion.m
+++ b/SignalServiceKit/src/Util/AppVersion.m
@@ -1,10 +1,12 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "AppVersion.h"
 #import <SignalServiceKit/NSUserDefaults+OWS.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 NSString *const kNSUserDefaults_FirstAppVersion = @"kNSUserDefaults_FirstAppVersion";
 NSString *const kNSUserDefaults_LastAppVersion = @"kNSUserDefaults_LastVersion";
 NSString *const kNSUserDefaults_LastCompletedLaunchAppVersion = @"kNSUserDefaults_LastCompletedLaunchAppVersion";
@@ -16,12 +18,12 @@ NSString *const kNSUserDefaults_LastCompletedLaunchAppVersion_SAE
 @interface AppVersion ()
 
 @property (atomic) NSString *firstAppVersion;
-@property (atomic) NSString *lastAppVersion;
+@property (atomic, nullable) NSString *lastAppVersion;
 @property (atomic) NSString *currentAppVersion;
 
-@property (atomic) NSString *lastCompletedLaunchAppVersion;
-@property (atomic) NSString *lastCompletedLaunchMainAppVersion;
-@property (atomic) NSString *lastCompletedLaunchSAEAppVersion;
+@property (atomic, nullable) NSString *lastCompletedLaunchAppVersion;
+@property (atomic, nullable) NSString *lastCompletedLaunchMainAppVersion;
+@property (atomic, nullable) NSString *lastCompletedLaunchSAEAppVersion;
 
 @end
 
@@ -126,3 +128,5 @@ NSString *const kNSUserDefaults_LastCompletedLaunchAppVersion_SAE
 }
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Util/FunctionalUtil.h b/SignalServiceKit/src/Util/FunctionalUtil.h
index 4b4fd0c48..1bb032c4d 100644
--- a/SignalServiceKit/src/Util/FunctionalUtil.h
+++ b/SignalServiceKit/src/Util/FunctionalUtil.h
@@ -1,7 +1,9 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface NSArray (FunctionalUtil)
 
 /// Returns true when any of the items in this array match the given predicate.
@@ -19,3 +21,5 @@
 - (NSDictionary *)groupBy:(id (^)(id value))keySelector;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Util/FunctionalUtil.m b/SignalServiceKit/src/Util/FunctionalUtil.m
index 8065d6cc5..830b47812 100644
--- a/SignalServiceKit/src/Util/FunctionalUtil.m
+++ b/SignalServiceKit/src/Util/FunctionalUtil.m
@@ -1,21 +1,27 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "FunctionalUtil.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface FUBadArgument : NSException
+
 + (FUBadArgument *) new:(NSString *)reason;
 + (void)raise:(NSString *)message;
+
 @end
 
 @implementation FUBadArgument
+
 + (FUBadArgument *) new:(NSString *)reason {
     return [[FUBadArgument alloc] initWithName:@"Invalid Argument" reason:reason userInfo:nil];
 }
 + (void)raise:(NSString *)message {
     [FUBadArgument raise:@"Invalid Argument" format:@"%@", message];
 }
+
 @end
 
 #define tskit_require(expr)                                                                                            \
@@ -85,4 +91,7 @@
 
     return result;
 }
+
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Util/NSData+Image.h b/SignalServiceKit/src/Util/NSData+Image.h
index 4e353a0cd..8ba02fff3 100644
--- a/SignalServiceKit/src/Util/NSData+Image.h
+++ b/SignalServiceKit/src/Util/NSData+Image.h
@@ -1,7 +1,9 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface NSData (Image)
 
 // If mimeType is non-nil, we ensure that the magic numbers agree with the
@@ -19,3 +21,5 @@
 + (BOOL)hasAlphaForValidImageFilePath:(NSString *)filePath;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Util/NSData+Image.m b/SignalServiceKit/src/Util/NSData+Image.m
index 4ba9b9673..13610f8ab 100644
--- a/SignalServiceKit/src/Util/NSData+Image.m
+++ b/SignalServiceKit/src/Util/NSData+Image.m
@@ -1,5 +1,5 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "NSData+Image.h"
@@ -8,6 +8,8 @@
 #import <AVFoundation/AVFoundation.h>
 #import <SignalServiceKit/SignalServiceKit-Swift.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 typedef NS_ENUM(NSInteger, ImageFormat) {
     ImageFormat_Unknown,
     ImageFormat_Png,
@@ -403,3 +405,5 @@ typedef NS_ENUM(NSInteger, ImageFormat) {
 }
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Util/NSURLSessionDataTask+StatusCode.h b/SignalServiceKit/src/Util/NSURLSessionDataTask+StatusCode.h
index d7989d04f..58067be8b 100644
--- a/SignalServiceKit/src/Util/NSURLSessionDataTask+StatusCode.h
+++ b/SignalServiceKit/src/Util/NSURLSessionDataTask+StatusCode.h
@@ -1,9 +1,13 @@
 //
-//  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface NSURLSessionTask (StatusCode)
 
 - (long)statusCode;
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Util/NSURLSessionDataTask+StatusCode.m b/SignalServiceKit/src/Util/NSURLSessionDataTask+StatusCode.m
index 82d4de438..212eeac55 100644
--- a/SignalServiceKit/src/Util/NSURLSessionDataTask+StatusCode.m
+++ b/SignalServiceKit/src/Util/NSURLSessionDataTask+StatusCode.m
@@ -1,13 +1,11 @@
 //
-//  NSURLSessionDataTask+StatusCode.m
-//  TextSecureKit
-//
-//  Created by Frederic Jacobs on 04/11/14.
-//  Copyright (c) 2014 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "NSURLSessionDataTask+StatusCode.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @implementation NSURLSessionTask (StatusCode)
 
 - (long)statusCode {
@@ -16,3 +14,5 @@
 }
 
 @end
+
+NS_ASSUME_NONNULL_END
diff --git a/SignalServiceKit/src/Util/UIImage+OWS.m b/SignalServiceKit/src/Util/UIImage+OWS.m
index 69c78784f..dd303a7aa 100644
--- a/SignalServiceKit/src/Util/UIImage+OWS.m
+++ b/SignalServiceKit/src/Util/UIImage+OWS.m
@@ -1,9 +1,11 @@
 //
-//  Copyright (c) 2018 Open Whisper Systems. All rights reserved.
+//  Copyright (c) 2019 Open Whisper Systems. All rights reserved.
 //
 
 #import "UIImage+OWS.h"
 
+NS_ASSUME_NONNULL_BEGIN
+
 @implementation UIImage (normalizeImage)
 
 - (UIImage *)normalizedImage
@@ -236,3 +238,5 @@
 }
 
 @end
+
+NS_ASSUME_NONNULL_END