THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
Specifying output schema for a UDF returns a tuple has been changed
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Before 0.12, There are two ways to specify tuple output schema for a UDF:
1. Returning a schema contains a single tuple field
2. Returning a schema that containing more than one field and it will be understood as a tuple schema
However, the second way is not reliable. It sometimes works and sometimes not. So in 0.12.0, we drop the second way and only the first way works.
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