[SPARK-28321][DOCS][FOLLOW-UP] Update migration guide by 0-args Java UDF's internal behaviour change#25224

HyukjinKwon wants to merge 2 commits intoapache:masterapache/spark:masterfrom

HyukjinKwon:SPARK-28321-docHyukjinKwon/spark:SPARK-28321-docCopy head branch name to clipboard