presto-main/src/main/java/io/prestosql/operator/scalar/ArrayUnionFunction.java/ArrayUnionFunction/bigintUnion
class ArrayUnionFunction:    @SqlType("array(bigint)")
    public static Block bigintUnion(@SqlType("array(bigint)") Block leftArray, @SqlType("array(bigint)") Block rightArray)
    {
        int leftArrayCount = leftArray.getPositionCount();
        int rightArrayCount = rightArray.getPositionCount();
        LongSet set = new LongOpenHashSet(leftArrayCount + rightArrayCount);
        BlockBuilder distinctElementBlockBuilder = BIGINT.createBlockBuilder(null, leftArrayCount + rightArrayCount);
        AtomicBoolean containsNull = new AtomicBoolean(false);
        appendBigintArray(leftArray, containsNull, set, distinctElementBlockBuilder);
        appendBigintArray(rightArray, containsNull, set, distinctElementBlockBuilder);

        return distinctElementBlockBuilder.build();
    }