Purge all compiler warnings

The vast majority are simply the compiler being confused about the signature saying "not null" and then an immediate check if the value is null or not.  It errs on the safe side and issues warnings about a possible null value on some platforms but not others.  The compiler will let you know if you are potentially passing a null to a method that cannot accept it, and so the null checks are all less important now.

Also fill in missing doc comments and update all bad refs between doc pages (including changes to gen_defaults.py)

src/Couchbase.Lite.Shared/API/DI/IReachability.cs

@@ -20,24 +20,40 @@
 
 namespace Couchbase.Lite.DI
 {
+ /// <summary>
+ /// An interface for describing whether a given URL is reachable via
+ /// network connection or not.
+ /// </summary>
  public interface IReachability
  {
  #region Variables
 
+ /// <summary>
+ /// Fired when the status of connectivity changes
+ /// </summary>
  event EventHandler<NetworkReachabilityChangeEventArgs> StatusChanged;
 
  #endregion
 
  #region Properties
 
+ /// <summary>
+ /// The URL to track connectivity to
+ /// </summary>
  Uri? Url { get; set; }
 
  #endregion
 
  #region Public Methods
 
+ /// <summary>
+ /// Start monitoring for changes in network status
+ /// </summary>
  void Start();
 
+ /// <summary>
+ /// Stop monitoring for changes in network status
+ /// </summary>
  void Stop();
 
  #endregion

src/Couchbase.Lite.Shared/API/Database/Collection.cs

@@ -817,7 +817,6 @@ private void PurgeDocById(string id)
  private bool Save(Document document, Document? baseDocument,
  ConcurrencyControl concurrencyControl, bool deletion)
  {
- Debug.Assert(document != null);
  if (deletion && document.RevisionID == null) {
  throw new CouchbaseLiteException(C4ErrorCode.NotFound,
  CouchbaseLiteErrorMessage.DeleteDocFailedNotSaved);

src/Couchbase.Lite.Shared/API/Database/CollectionChangedEventArgs.cs

@@ -43,7 +43,6 @@ public sealed class CollectionChangedEventArgs : DatabaseChangedEventArgs
  Database database)
  :base(database, documentIDs)
  {
- Debug.Assert(collection != null);
  Collection = collection;
  }
 

src/Couchbase.Lite.Shared/API/Database/Database.cs

@@ -1178,8 +1178,6 @@ internal bool SaveCookie(string cookie, Uri uri, bool acceptParentDomain)
 
  internal void ResolveConflict(string docID, IConflictResolver? conflictResolver, Collection collection)
  {
- Debug.Assert(docID != null);
-
  var writeSuccess = false;
  while (!writeSuccess) {
  var readSuccess = false;
@@ -1284,7 +1282,7 @@ private static string DatabasePath(string? directory)
  CouchbaseLiteErrorMessage.ResolveDefaultDirectoryFailed);
  }
 
- return directoryToUse;
+ return directoryToUse!;
  }
 
  private static string DatabasePath(string name, string? directory)

src/Couchbase.Lite.Shared/API/Database/DatabaseChangedEventArgs.cs

@@ -47,9 +47,6 @@ public class DatabaseChangedEventArgs : EventArgs
 
  internal DatabaseChangedEventArgs(Database database, IReadOnlyList<string> documentIDs)
  {
- Debug.Assert(database != null);
- Debug.Assert(documentIDs != null);
- Debug.Assert(documentIDs.All(x => x != null));
  Database = database;
  DocumentIDs = documentIDs;
  }

src/Couchbase.Lite.Shared/API/Document/Blob.cs

@@ -370,8 +370,6 @@ internal bool JSONEquals(Dictionary<string, object> obj)
 
  internal void Install(Database db)
  {
- Debug.Assert(db != null);
-
  if (Digest != null && _db == null) {
  _db = db;
  }

src/Couchbase.Lite.Shared/API/Document/Document.cs

@@ -62,15 +62,15 @@ public unsafe class Document : IDictionaryObject, IJSON, IDisposable
  {
  get {
  Debug.Assert(Database != null && Database.c4db != null);
- return Database.c4db;
+ return Database!.c4db;
  }
  }
 
  internal C4Collection* c4Coll
  {
  get {
  Debug.Assert(Collection != null && Collection.c4coll != null);
- return Collection.c4coll;
+ return Collection!.c4coll;
  }
  }
 
@@ -165,8 +165,6 @@ public unsafe class Document : IDictionaryObject, IJSON, IDisposable
 
  internal Document(Collection? collection, string id, C4DocumentWrapper? c4Doc)
  {
- Debug.Assert(id != null);
-
  Collection = collection;
  Id = id;
  this.c4Doc = c4Doc;
@@ -196,8 +194,6 @@ internal Document(Collection? collection, string id, string revId, FLDict* body)
  internal Document(Document other)
  : this(other.Collection, other.Id, other.c4Doc?.Retain<C4DocumentWrapper>())
  {
- Debug.Assert(other != null);
-
  if(other._root != null) {
  _root = new MRoot(other._root);
  } else {
@@ -292,7 +288,7 @@ private void UpdateDictionary()
  if (Data != null) {
  Debug.Assert(Database != null);
  Misc.SafeSwap(ref _root,
- new MRoot(new DocContext(Database, _c4Doc), (FLValue*) Data, IsMutable));
+ new MRoot(new DocContext(Database!, _c4Doc), (FLValue*) Data, IsMutable));
  Collection?.ThreadSafety?.DoLocked(() => _dict = (DictionaryObject?) _root!.AsObject());
  } else {
  Misc.SafeSwap(ref _root, null);

src/Couchbase.Lite.Shared/API/Document/MutableDocument.cs

@@ -205,7 +205,7 @@ internal override FLSliceResult Encode()
  Debug.Assert(Database != null);
 
  var body = new FLSliceResult();
- Database.ThreadSafety.DoLocked(() =>
+ Database!.ThreadSafety.DoLocked(() =>
  {
  FLEncoder* encoder = null;
  try {