validator for custom field not working

[Sander Groenen]

we are evaluating script runner plugin. But we have all kinds of issues. One specific issue is i want a validator that checks a customfield value but it seems like the value is not retrieved (null). And by the way in script console i cannot check the output because either it returns some kind of impersonation oauth error or issue not found where i can retrieve it by using postman rest api

the validtor rule is for example : issue.customfield_10749.plainText== 'test' which returns false when tested against issue. However when doing issue.customfield_10749.plainText only it returns null in the view results output. Where for example description.plainText (jira default field)does return te text entered

in curl request i have to do api/2/issue/V2-2560?expand=customfield_010749 

(with expand) to get value of the field otherwise its null so im guessing this could be the problem. Also i don't understand why i have to use the plainText property, what i could see/find is that just the customfield_xxx should return the string but this gives a wrong operator error. 

any tips are appreciated