Describe the bug

Please close if this is intended: currently the null_count in Statistics defaults to 0 and the has_nulls() is based on null_count > 0, leading to ambiguity when null_count equals 0: either all values are non-null, or just that the null count stat is missing.

To Reproduce
n/a

Expected behavior

it feels reasonable to distinguish no null and null_count not set.

Additional context
n/a