Using ProxySQL 2.7.0-11-g3835029 I sometimes get spaces in the digest:

SELECT * FROM workshop_labour_unavailable WHERE Type = 'Workshop' AND Depot = 'STOCK';

Gives a digest of: 0x 6E817ACFD8D15DC

Inserting this into mysql_query_rules results in NULL, causing it to match everything.

Deleting the space works as expected.