getting error in log files in jira

[Pankaj Mehta]

This is code :

11. cfList.find { it ->

23. globalActType = parent?.concat("_").concat(child)

-------------x-----------------x---------------------x------------------x-------------------x-------

This beolw error is showing in log files:

[c.o.scriptrunner.customfield.GroovyCustomField] Script field failed on issue: ABC-1001, field: Global Activity Type
java.lang.NullPointerException
	at java_lang_String$concat$14.call(Unknown Source)
	at scripts.scriptedfields.GlobalActivityType$_run_closure1.doCall(GlobalActivityType.groovy:23)
	at scripts.scriptedfields.GlobalActivityType.run(GlobalActivityType.groovy:11)
[c.o.scriptrunner.customfield.GroovyCustomField]

 can anyone tell  me what is the cause for that above error ?

Thanks.

[Nic Brough -Adaptavist-]

Look at the rest of the error - it should tell you which line in your script is making the call to the Jira API that is throwing that snippet. 

People generally won't want to read your entire code to understand it and then looking for errors, when you could just tell us what line starts the error off