Exeption while generating hmac for filter with NULL or empty values

[simonschaufi]

i have 2 tables. table A and table B.
I want to join table A with table B with field x
x has NULL values and integers
I created a checkbox filter to group all values of field x and filter for that field.
my SQL looks like this:
SELECT tableA.id, tableA.x
FROM tableA LEFT JOIN tableB ON tableA.x = tableB.id

the moment i remove all entries from tableA where x is NULL or empty string, then the filter works.

Hint: I'm accessing an external database, I know that TYPO3 tables usually use 0 as default value instead of NULL value.

right now i have no glue how this can be fixed otherwise I would have done a pull request already ;)