presto-main/src/main/java/io/prestosql/operator/unnest/ArrayOfRowsUnnester.java/ArrayOfRowsUnnester/getInputEntryCount
class ArrayOfRowsUnnester:    @Override
    int getInputEntryCount()
    {
        if (columnarArray == null) {
            return 0;
        }
        return columnarArray.getPositionCount();
    }