fix: unit tests various

Author: maurei

src/JsonApiDotNetCore/Serialization/Common/BaseDocumentParser.cs

@@ -96,9 +96,7 @@ protected IIdentifiable SetRelationships(IIdentifiable entity, Dictionary<string
             var entityProperties = entity.GetType().GetProperties();
             foreach (var attr in relationshipAttributes)
             {
-                relationshipsValues.TryGetValue(attr.PublicRelationshipName, out RelationshipData relationshipData);
-
-                if (relationshipData == null || !relationshipData.HasData)
+                if (!relationshipsValues.TryGetValue(attr.PublicRelationshipName, out RelationshipData relationshipData) || !relationshipData.IsPopulated)
                     continue;
 
                 if (attr is HasOneAttribute hasOne)
@@ -120,7 +118,6 @@ private JToken LoadJToken(string body)
             return jToken;
         }
 
-
         /// <summary>
         /// Creates an instance of the referenced type in <paramref name="data"/>
         /// and sets its attributes and relationships
@@ -227,15 +224,18 @@ private object SetHasManyRelationship(IIdentifiable entity,
                                               HasManyAttribute attr,
                                               RelationshipData relationshipData)
         {
-            var relatedResources = relationshipData.ManyData.Select(rio =>
-            {
-                var relatedInstance = attr.DependentType.New<IIdentifiable>();
-                relatedInstance.StringId = rio.Id;
-                return relatedInstance;
-            });
+            if (relationshipData.Data != null)
+            {   // if the relationship is set to null, no need to set the navigation property to null: this is the default value.
+                var relatedResources = relationshipData.ManyData.Select(rio =>
+                {
+                    var relatedInstance = attr.DependentType.New<IIdentifiable>();
+                    relatedInstance.StringId = rio.Id;
+                    return relatedInstance;
+                });
+                var convertedCollection = TypeHelper.ConvertCollection(relatedResources, attr.DependentType);
+                attr.SetValue(entity, convertedCollection);
+            }
 
-            var convertedCollection = TypeHelper.ConvertCollection(relatedResources, attr.DependentType);
-            attr.SetValue(entity, convertedCollection);
             AfterProcessField(entity, attr, relationshipData);
 
             return entity;

test/UnitTests/Serialization/Common/DocumentParserTests.cs

@@ -270,7 +270,7 @@ public void DeserializeRelationships_EmptyRequiredOneToOnePrincipal_ThrowsFormat
             var body = JsonConvert.SerializeObject(content);
 
             // act, assert
-            Assert.ThrowsAny<FormatException>(() => _deserializer.Deserialize(body));
+            Assert.Throws<FormatException>(() => _deserializer.Deserialize(body));
         }
 
         [Fact]
@@ -316,7 +316,7 @@ public void DeserializeRelationships_EmptyOneToManyRequiredPrincipal_ThrowsForma
             var body = JsonConvert.SerializeObject(content);
 
             // act, assert
-            Assert.ThrowsAny<FormatException>(() => _deserializer.Deserialize(body));
+            Assert.Throws<FormatException>(() => _deserializer.Deserialize(body));
         }
 
         [Fact]