- fixes a null reference exception on implicit nav props detection

Author: baywet

src/GraphODataTemplateWriter/Extensions/OdcmModelExtensions.cs

@@ -257,18 +257,18 @@ public static OdcmProperty GetServiceCollectionNavigationPropertyForPropertyType
                             @namespace
                             .Classes
                             .Where(odcmClass => odcmClass.Kind == OdcmClassKind.Service)
-                            .First()
-                            .Properties
-                            .Where(property => property.GetType() == typeof(OdcmSingleton)) //Get the list of singletons defined by the service
-                            .Where(singleton => singleton
+                            .FirstOrDefault()
+                            ?.Properties
+                            ?.Where(property => property.GetType() == typeof(OdcmSingleton)) //Get the list of singletons defined by the service
+                            ?.Where(singleton => singleton
                                 .Type
                                 .AsOdcmClass()
                                 .Properties
                                 //Find navigation properties on the singleton that are self-contained (implicit EntitySets) that match the type
                                 //we are searching for
                                 .Where(prop => prop.ContainsTarget == true && prop.Type.Name == odcmProperty.Type.Name)
                                 .FirstOrDefault() != null
-                             )
+                             ) ?? new OdcmProperty[] { }
                          ).FirstOrDefault();
 
                     if (implicitProperty != null)