Don't crash when contact lookup is given nil contact

// FREEBIE

src/Contacts/ContactsUpdater.m

@@ -1,16 +1,12 @@
-//
-//  ContactsManager+updater.m
-//  Signal
-//
 //  Created by Frederic Jacobs on 21/11/15.
 //  Copyright © 2015 Open Whisper Systems. All rights reserved.
-//
 
 #import "ContactsUpdater.h"
 
 #import "Contact.h"
 #import "Cryptography.h"
 #import "PhoneNumber.h"
+#import "OWSError.h"
 #import "TSContactsIntersectionRequest.h"
 #import "TSNetworkManager.h"
 #import "TSStorageManager.h"
@@ -63,7 +59,14 @@
 
 - (void)lookupIdentifier:(NSString *)identifier
                  success:(void (^)(NSSet<NSString *> *matchedIds))success
-                 failure:(void (^)(NSError *error))failure {
+                 failure:(void (^)(NSError *error))failure
+{
+    if(!identifier) {
+        NSError *error = OWSErrorWithCodeDescription(1, @"Cannot lookup nil identifier");
+        BLOCK_SAFE_RUN(failure, error);
+        return;
+    }
+
     [self contactIntersectionWithSet:[NSSet setWithObject:identifier]
         success:^(NSSet<NSString *> *matchedIds) {
           BLOCK_SAFE_RUN(success, matchedIds);

src/Messages/TSMessagesManager+sendMessages.m

@@ -139,9 +139,11 @@ dispatch_queue_t sendingQueue() {
                       }
                       failure:^(NSError *error) {
                         if (error.code == NOTFOUND_ERROR) {
+                            DDLogWarn(@"recipient contact not found with error: %@", error);
                             [self unregisteredRecipient:recipient message:message inThread:thread];
                             return;
                         } else {
+                            DDLogError(@"contact lookup failed with error: %@", error);
                             [self saveMessage:message withState:TSOutgoingMessageStateUnsent];
                             return;
                         }

src/Util/OWSError.h

@@ -0,0 +1,9 @@
+//  Copyright © 2016 Open Whisper Systems. All rights reserved.
+
+NS_ASSUME_NONNULL_BEGIN
+
+extern NSString *const OWSSignalServiceKitErrorDomain;
+
+extern NSError *OWSErrorWithCodeDescription(NSInteger code, NSString *description);
+
+NS_ASSUME_NONNULL_END

src/Util/OWSError.m

@@ -0,0 +1,16 @@
+//  Copyright © 2016 Open Whisper Systems. All rights reserved.
+
+#import "OWSError.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+NSString *const OWSSignalServiceKitErrorDomain = @"OWSSignalServiceKitErrorDomain";
+
+NSError *OWSErrorWithCodeDescription(NSInteger code, NSString *description)
+{
+    return [NSError errorWithDomain:OWSSignalServiceKitErrorDomain
+                               code:code
+                           userInfo:@{ NSLocalizedDescriptionKey: description }];
+}
+
+NS_ASSUME_NONNULL_END