SAK-42721: check that assignment url is not empty string (#7622)
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SAK-42721: check that assignment url is not empty string
(cherry picked from commit d8114ba2f09fb97deab9d4ca6df4ee4a61d067f7)
Conflicts:
portal/portal-api/api/src/java/org/sakaiproject/portal/beans/bullhornhandlers/GradeAssignmentBullhornHandler.java