[BUG] explode_outer_position doesn't match to Spark's counterpart

[sperlingxx]

Describe the bug
In cuDF, explode_outer_position will mark the position values of empty rows with 0. Meanwhile, the position values of empty rows are marked as null in Spark.

Steps/Code to reproduce bug
For input data like:

• [[5,null,15], 100]
• [null, 200]
• [[], 300]

cuDF returns

• [0, 5, 100]
• [1, null, 100]
• [2, 15, 100]
• [0, null, 200]
• [0, null, 300]

But Spark returns

• [0, 5, 100]
• [1, null, 100]
• [2, 15, 100]
• [null, null, 200]
• [null, null, 300]

[hyperbolic2346]

I assume this holds for explode_position as well?

[sperlingxx]

I assume this holds for explode_position as well?

I think current explode_position implementation is identicial to Spark, since the empty/null elements of array will be regarded as other values.