1. Create event correlation:
2. add a condition of any type and any value;
3. add a second condition of any type and any value;
4. change type of calculation to custom formula;
5. enter A and B in expression;
6. remove on of the conditions;
7. observe custom formula field is gone;
8. try to save event correlation;
Result: Error Invalid parameter "/1/filter/conditions/1": unexpected parameter "formulaid".
Expected: since there is no custom formula field and only one condition remains, the correlation should be successfully saved.