presto-main/src/main/java/io/prestosql/operator/scalar/RepeatFunction.java/RepeatFunction/repeatNullValues
class RepeatFunction:    private static Block repeatNullValues(BlockBuilder blockBuilder, long count)
    {
        for (int i = 0; i < count; i++) {
            blockBuilder.appendNull();
        }
        return blockBuilder.build();
    }