HiveUdfCall has the sizes of internal types hardcoded as magic numbers:
STRING and VARCHAR were only 16 bytes because of padding. This padding is removed by
IMPALA-7367, so this will read past the end of the actual value. This could in theory lead to a crash.
We need to change the value, but we should probably also switch to sizeof(StringValue) so that it doesn't get broken by similar changes in future.