ObjectRelationType: also set type2enabled_proxy on empty string

entity/ObjectRelationType_entity/entityfields/type2enabled_proxy/valueProcess.js

 import("system.vars");
 import("system.result");
 
-if (vars.get("$this.value") == null)
+if (vars.get("$this.value") == null || vars.get("$this.value") == "")
     result.string(vars.get("$field.DIRECTION") == "same" ? 0 : 1);
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