Merge pull request #854 from microsoftgraph/fixgeneration

Fix null reference exception when method return type is an odata primitive.

Author: andrueastman

src/GraphODataTemplateWriter/Extensions/OdcmModelExtensions.cs

@@ -730,10 +730,10 @@ public static List<OdcmProperty> GetComposableFunctionReturnTypeNavigations(this
                 throw new InvalidOperationException("This extension method is intended " +
                                                     "to only be called on a composable function.");
 
-            return (odcmMethod.ReturnType as OdcmClass).Properties
+            return (odcmMethod.ReturnType as OdcmClass)?.Properties
                                                        .Where(p => p.IsLink)
                                                        .OrderBy(p => p.Name)
-                                                       .ToList();
+                                                       .ToList() ?? new List<OdcmProperty>(); // default to empty list
         }
 
         /// <summary>