approx_percentile cast error

[okennedy]

Describe the bug
Use of the approximate percentile function appears to force an incorrect cast to string.

To Reproduce
Create a dataset R with a column A

select avg(a), approx_percentile(a, array(0.5)) FROM R

Expected behavior
No exception

[okennedy]

cannot resolve 'percentile(midterm1.out_of_100, applycaveat(CAST(0.25BD AS DOUBLE), concat('Could not cast \'', coalesce(CAST(0.25BD AS STRING), '\'NULL\''), '\' to DoubleType (in 0.25)'), ((NOT (0.25BD IS NULL)) AND (CAST(0.25BD AS DOUBLE) IS NULL))), 1L)' due to data type mismatch: The percentage(s) must be a constant literal, but got applycaveat(cast(0.25 as double), concat(Could not cast ', coalesce(cast(0.25 as string), 'NULL'), ' to DoubleType (in 0.25)), None, false, (NOT isnull(0.25) AND isnull(cast(0.25 as double))))