Add missing null checks

Author: bkoelman

src/JsonApiDotNetCore/Queries/FieldSelectors.cs

@@ -52,9 +52,10 @@ public void IncludeAttributes(IEnumerable<AttrAttribute> attributes)
         }
     }
 
-    public void IncludeRelationship(RelationshipAttribute relationship, QueryLayer? queryLayer)
+    public void IncludeRelationship(RelationshipAttribute relationship, QueryLayer queryLayer)
     {
         ArgumentGuard.NotNull(relationship);
+        ArgumentGuard.NotNull(queryLayer);
 
         this[relationship] = queryLayer;
     }

src/JsonApiDotNetCore/Repositories/EntityFrameworkCoreRepository.cs

@@ -163,6 +163,8 @@ public virtual Task<TResource> GetForCreateAsync(Type resourceClrType, TId id, C
             id
         });
 
+        ArgumentGuard.NotNull(resourceClrType);
+
         var resource = (TResource)_resourceFactory.CreateInstance(resourceClrType);
         resource.Id = id;