Hi @clemens-msupply,
In the cases were the behavior for not set properties does not match your expectation you can often just reverse the rule, i.e. design it as a DISABLE and revert the condition schema with a not.
In case you want to be more explicit or would like to have more control you can modify the condition scope to the parent scope, in your case # and then go into more detail in regards to stringArray itself, for example by setting it to required in the condition schema.
@dcjarvisvt’s suggestion works around the problem by always making sure that stringArray is defined, however I would recommend setting the default to the empty array.