logic hole in obscure case in MetaDataObject_impl

While reviewing the changes in MetaDataObject_impl, I noticed a path in writePrimitiveValue, which wraps the primitive value with an "element-kind", like <element-kind>value</element-kind>. For JSON serialization, this is

. But for JSON this wrapping is not done if the value is a string. There's a logic bug in this case (which may not occur in practice?) - the skipping of the writing of the closing } is not done, needs fixing.