Respond to CR.

// FREEBIE

Signal/src/util/ThreadUtil.h

@@ -2,12 +2,12 @@
 //  Copyright (c) 2017 Open Whisper Systems. All rights reserved.
 //
 
-#import <Foundation/Foundation.h>
-
 @class TSThread;
 @class OWSMessageSender;
 @class SignalAttachment;
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface ThreadUtil : NSObject
 
 + (void)sendMessageWithText:(NSString *)text
@@ -19,3 +19,5 @@
                     messageSender:(OWSMessageSender *)messageSender;
 
 @end
+
+NS_ASSUME_NONNULL_END

Signal/src/util/ThreadUtil.m

@@ -10,6 +10,8 @@
 #import <SignalServiceKit/TSOutgoingMessage.h>
 #import <SignalServiceKit/TSThread.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 @implementation ThreadUtil
 
 + (void)sendMessageWithText:(NSString *)text inThread:(TSThread *)thread messageSender:(OWSMessageSender *)messageSender
@@ -95,3 +97,5 @@
 }
 
 @end
+
+NS_ASSUME_NONNULL_END

Signal/src/view controllers/DebugUITableViewController.m

@@ -15,7 +15,7 @@ NS_ASSUME_NONNULL_BEGIN
 @interface OWSTableContents : NSObject
 
 @property (nonatomic) NSString *title;
-@property (nonatomic) NSMutableArray *sections;
+@property (nonatomic) NSMutableArray<OWSTableSection *> *sections;
 
 @end
 
@@ -23,12 +23,15 @@ NS_ASSUME_NONNULL_BEGIN
 
 @implementation OWSTableContents
 
-- (void)addSection:(OWSTableSection *)section {
-    OWSAssert(section);
-    
-    if (!_sections) {
+-(instancetype)init {
+    if (self = [self init]) {
         _sections = [NSMutableArray new];
     }
+    return self;
+}
+
+- (void)addSection:(OWSTableSection *)section {
+    OWSAssert(section);
     
     [_sections addObject:section];
 }
@@ -40,7 +43,7 @@ NS_ASSUME_NONNULL_BEGIN
 @interface OWSTableSection : NSObject
 
 @property (nonatomic) NSString *title;
-@property (nonatomic) NSMutableArray *items;
+@property (nonatomic) NSMutableArray<OWSTableItem *> *items;
 
 @end
 
@@ -56,6 +59,13 @@ NS_ASSUME_NONNULL_BEGIN
     return section;
 }
 
+-(instancetype)init {
+    if (self = [self init]) {
+        _items = [NSMutableArray new];
+    }
+    return self;
+}
+
 - (void)addItem:(OWSTableItem *)item {
     OWSAssert(item);