fix: compare unresolved references by $ref and resolve bindings Extensions

Unresolved references compared their null targets, so every unresolved
reference equalled every other one and equalled null. They now compare
by their $ref string, and comparing with a null element returns false.
Resolved references compare as before.

AsyncApiReference overrode Equals without GetHashCode; it now hashes its
$ref string. AsyncApiBindingsReference.Extensions read the backing field,
so it threw until another member had resolved the reference.

Author: VisualBean

src/ByteBard.AsyncAPI/Models/AsyncApiReference.cs

@@ -151,6 +151,11 @@ public override bool Equals(object obj)
             return this.Equals(reference);
         }
 
+        public override int GetHashCode()
+        {
+            return this.Reference?.GetHashCode() ?? 0;
+        }
+
         /// <summary>
         /// Serialize <see cref="AsyncApiReference"/> to Async Api.
         /// </summary>

src/ByteBard.AsyncAPI/Models/References/AsyncApiBindingsReference{TBinding}.cs

@@ -34,7 +34,7 @@ public override void Add(TBinding binding)
 
         public override ICollection<TBinding> Values => this.Target.Values;
 
-        public override IDictionary<string, IAsyncApiExtension> Extensions => this.target.Extensions;
+        public override IDictionary<string, IAsyncApiExtension> Extensions => this.Target.Extensions;
 
         public override int Count => this.Target.Count;
 

src/ByteBard.AsyncAPI/Models/References/AsyncApiChannelReference.cs

@@ -98,6 +98,11 @@ public bool Equals(AsyncApiChannelReference other)
                 return this.Equals(reference);
             }
 
+            if (this.Target is null && other.Target is null)
+            {
+                return this.Reference == other.Reference;
+            }
+
             return this.Target == other.Target;
         }
 
@@ -118,7 +123,7 @@ public override bool Equals(object obj)
 
         public bool Equals(AsyncApiChannel other)
         {
-            return this.Target == other;
+            return other is not null && this.Target == other;
         }
     }
 }

src/ByteBard.AsyncAPI/Models/References/AsyncApiCorrelationIdReference.cs

@@ -58,6 +58,11 @@ public bool Equals(AsyncApiCorrelationIdReference other)
                 return this.Equals(reference);
             }
 
+            if (this.Target is null && other.Target is null)
+            {
+                return this.Reference == other.Reference;
+            }
+
             return this.Target == other.Target;
         }
 
@@ -78,7 +83,7 @@ public override bool Equals(object obj)
 
         public bool Equals(AsyncApiCorrelationId other)
         {
-            return this.Target == other;
+            return other is not null && this.Target == other;
         }
 
         public override void SerializeV2(IAsyncApiWriter writer)

src/ByteBard.AsyncAPI/Models/References/AsyncApiExternalDocumentationReference.cs

@@ -54,6 +54,11 @@ public bool Equals(AsyncApiExternalDocumentationReference other)
                 return this.Equals(reference);
             }
 
+            if (this.Target is null && other.Target is null)
+            {
+                return this.Reference == other.Reference;
+            }
+
             return this.Target == other.Target;
         }
 
@@ -74,7 +79,7 @@ public override bool Equals(object obj)
 
         public bool Equals(AsyncApiExternalDocumentation other)
         {
-            return this.Target == other;
+            return other is not null && this.Target == other;
         }
 
         /// <summary>

src/ByteBard.AsyncAPI/Models/References/AsyncApiJsonSchemaReference.cs

@@ -309,6 +309,11 @@ public bool Equals(AsyncApiJsonSchemaReference other)
                 return this.Equals(reference);
             }
 
+            if (this.Target is null && other.Target is null)
+            {
+                return this.Reference == other.Reference;
+            }
+
             return this.Target == other.Target;
         }
 
@@ -329,7 +334,7 @@ public override bool Equals(object obj)
 
         public bool Equals(AsyncApiJsonSchema other)
         {
-            return this.Target == other;
+            return other is not null && this.Target == other;
         }
 
         public override void SerializeV2(IAsyncApiWriter writer)

src/ByteBard.AsyncAPI/Models/References/AsyncApiMessageReference.cs

@@ -79,6 +79,11 @@ public bool Equals(AsyncApiMessageReference other)
                 return this.Equals(reference);
             }
 
+            if (this.Target is null && other.Target is null)
+            {
+                return this.Reference == other.Reference;
+            }
+
             return this.Target == other.Target;
         }
 
@@ -99,7 +104,7 @@ public override bool Equals(object obj)
 
         public bool Equals(AsyncApiMessage other)
         {
-            return this.Target == other;
+            return other is not null && this.Target == other;
         }
 
         public override void SerializeV2(IAsyncApiWriter writer)

src/ByteBard.AsyncAPI/Models/References/AsyncApiMessageTraitReference.cs

@@ -76,6 +76,11 @@ public bool Equals(AsyncApiMessageTraitReference other)
                 return this.Equals(reference);
             }
 
+            if (this.Target is null && other.Target is null)
+            {
+                return this.Reference == other.Reference;
+            }
+
             return this.Target == other.Target;
         }
 
@@ -96,7 +101,7 @@ public override bool Equals(object obj)
 
         public bool Equals(AsyncApiMessageTrait other)
         {
-            return this.Target == other;
+            return other is not null && this.Target == other;
         }
 
         public override void SerializeV2(IAsyncApiWriter writer)

src/ByteBard.AsyncAPI/Models/References/AsyncApiOperationReference.cs

@@ -78,6 +78,11 @@ public bool Equals(AsyncApiOperationReference other)
                 return this.Equals(reference);
             }
 
+            if (this.Target is null && other.Target is null)
+            {
+                return this.Reference == other.Reference;
+            }
+
             return this.Target == other.Target;
         }
 
@@ -98,7 +103,7 @@ public override bool Equals(object obj)
 
         public bool Equals(AsyncApiOperation other)
         {
-            return this.Target == other;
+            return other is not null && this.Target == other;
         }
 
         public override void SerializeV2(IAsyncApiWriter writer)

src/ByteBard.AsyncAPI/Models/References/AsyncApiOperationReplyAddressReference.cs

@@ -54,6 +54,11 @@ public bool Equals(AsyncApiOperationReplyAddressReference other)
                 return this.Equals(reference);
             }
 
+            if (this.Target is null && other.Target is null)
+            {
+                return this.Reference == other.Reference;
+            }
+
             return this.Target == other.Target;
         }
 
@@ -74,7 +79,7 @@ public override bool Equals(object obj)
 
         public bool Equals(AsyncApiOperationReplyAddress other)
         {
-            return this.Target == other;
+            return other is not null && this.Target == other;
         }
 
         public override void SerializeV3(IAsyncApiWriter writer)