User account registration works only, if user image is not required

If I set the user image as required (field name: "user_picture"). Then I cannot login via facebook. There comes the error: Creation of user account failed: This value should not be null (I have translated the last part from german into english). However, if I set the user_picture field as "not" required, I can login succesfully via facebook and the user picture is retrieved. What I need to do, to keep the user picture required in the user profile field settings and still be able to login via facebook? Is this a bug in the "Simple FB Connect" module?

30 Apr 2017 ... User pictures are enabled but not required (Drupal default behavior); API call for getting the Facebook profile picture fails OR the profile picture ...

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