presto-main/src/main/java/io/prestosql/operator/scalar/ArrayUnionFunction.java/ArrayUnionFunction/appendBigintArray
class ArrayUnionFunction:    private static void appendBigintArray(Block array, AtomicBoolean containsNull, LongSet set, BlockBuilder blockBuilder)
    {
        for (int i = 0; i < array.getPositionCount(); i++) {
            if (array.isNull(i)) {
                if (!containsNull.get()) {
                    containsNull.set(true);
                    blockBuilder.appendNull();
                }
                continue;
            }
            long value = BIGINT.getLong(array, i);
            if (set.add(value)) {
                BIGINT.writeLong(blockBuilder, value);
            }
        }
    }