The bug
Using /execute if/unless score
and testing for players which do not have a score sets 0 for them and the test succeeds.
Expected would be that the comparison failed and no score was set.
How to reproduce
Create a new objective called something like test
Run the following to set the value to test with
/scoreboard players set value test 0
Run
/execute if score something test = value test run say test
❌ The command runs successfully even though the player "something" hasn't been initialized in the objective "test"
Confirmed