Value.Type() can return a reference to a nil pointer

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Issue to be solved

Current implementations of Value.Type() can return a Type referencing a nil pointer.

This can make callers deference the nil pointer.

Suggested Solution

Implementations of Value.Type() should return nil instead of a reference to a nil pointer.

Change Type() to check and return nil Type, instead of Type referencing nil pointer for these external values:

• Dictionary
• Struct
• Resource
• Attachment
• Event
• Contract
• Enum
• Function