Null check in GenerateExpandQueryStringInternal (#2795)

Author: KenitoInc

src/Microsoft.AspNet.OData.Shared/Query/ExpandQueryBuilder.cs

@@ -40,21 +40,33 @@ public virtual string GenerateExpandQueryParameter(object value, IEdmModel model
 
         private string GenerateExpandQueryStringInternal(object value, IEdmModel model, bool isNestedExpand)
         {
+            string expandString = "";
+
+            if (value == null || model == null)
+            {
+                return expandString;
+            }
+
             Type type = value.GetType();
             bool isCollection = TypeHelper.IsCollection(type, out Type elementType);
             IEnumerable collection = null;
+
             if (isCollection)
             {
                 type = elementType;
                 collection = value as IEnumerable;
             }
 
             string edmFullName = type.EdmFullName();
-            IEdmSchemaType schemaType = model.FindType(edmFullName);
-            IEdmStructuredType edmStructuredType = schemaType as IEdmStructuredType;
+
+            IEdmStructuredType edmStructuredType = model.FindType(edmFullName) as IEdmStructuredType;
+
+            if (edmStructuredType == null)
+            {
+                return expandString;
+            }
 
             IEnumerable<IEdmNavigationProperty> navigationProperties = edmStructuredType.NavigationProperties();
-            string expandString = "";
 
             int count = 0;