Undeclared enum type value for untype value serialized as empty resource

[xuzhg]

Assemblies affected
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Describe the bug
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Reproduce steps
If we have

public enum UserType {...}

But this enum is not defined in OData model.

Suppose we use this C# enum to assign a value for a untyped property or dynamic property, the result is empty resource.

Person p = new Person
{
    Data = UserType.Admin  // System.Object Data {get;set;}
}

We get:

"Data": {},

This is because, in "CreateUntypedPropertyValue", we can't get the Edm type for "UserType", then we consider it a resource.
So, goes to the resource serializer, owing that the enum type doesn't have public properties,
so, the final result is an empty resource.

Before the fix, the workaround is to call 'ToString'.

Person p = new Person
{
    Data = UserType.Admin.ToString()
}

Data Model
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EDM (CSDL) Model
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Expected behavior
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