Why the org.apache.spark.sql.catalyst.expressions.SortArray is with CodegenFallback?

I found CollapseCodengenStages.supportCodegen(e: Expression) will determine SortArray expression not CodegenSupported since SortArray is with CodegenFallback. Can I ask why the SortArray is not CodeGenSupoort??

Does schema merge on keys with different types is allowed?

The issue https://issues.apache.org/jira/browse/SPARK-15516 that is about schema merging on keys with different types need to be clarified. Does anyone know the behaviour of schema merging when encountering different types?