Scenario: call map() on an array that contains null values.
What I expected:
1) The new array should have the same length as the original array.
2) Each item in the new array should have the value returned from the map function.
What actually happened:
1) If the original array has nothing but null values, the new array has a length of 0.
2) If the original array contains a mix of null and non-null values, it is impossible to map the null values to a different value.
As this works on ACF 2018, can you add the acf-compat label?