java.lang.NullPointerException: null receiver

What this error mean ?

Line 192 is the latest line "End Sub" of
Private Sub JobDone (Job As HttpJob) in the class that downloads by OKHttputils2 built-in lib v.2.20 (not a class). B4A v.6.

Job is successful, but error in the end of the sub. And error only in DEBUG mode at first start, if to restart "running previous successful shell app" - NO ERROR ! Release looks OK, but sometimes the black screen and app is closed.
Job result is

Code:

  CallSubDelayed2(Client, "Refresh_tab", m)  

...

java.lang.NullPointerException: null receiver

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