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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_nullable_type(type_):
 # noqa: F811 """Unwrap possible non-null type"""

    if is_non_null_type(type_):
        type_ = cast(GraphQLNonNull, type_)
        type_ = type_.of_type
    return cast(Optional[GraphQLNullableType], type_)