fix: fix enrollment.has_started check (#31059)

Co-authored-by: nsprenkle <nsprenkle@2u.com>

lms/djangoapps/learner_home/serializers.py

@@ -194,7 +194,7 @@ class EnrollmentSerializer(serializers.Serializer):
         resume_button_url = self.context.get("resume_course_urls", {}).get(
             enrollment.course_id
         )
-        return resume_button_url is not None
+        return bool(resume_button_url)
 
     def get_isVerified(self, enrollment):
         return enrollment.is_verified_enrollment()

lms/djangoapps/learner_home/test_serializers.py

@@ -372,7 +372,7 @@ class TestEnrollmentSerializer(LearnerDashboardBaseTest):
         output = EnrollmentSerializer(input_data, context=input_context).data
         assert output["canUpgrade"] is True
 
-    @ddt.data(None, "some_url")
+    @ddt.data(None, "", "some_url")
     def test_has_started(self, resume_url):
         # Given the presence or lack of a resume_course_url
         input_data = self.create_test_enrollment()