Fix JS error that causes Step Builder to crash if no review step is present.

problem_builder/public/js/mentoring_with_steps.js

@@ -230,8 +230,10 @@ function MentoringWithStepsBlock(runtime, element) {
     }
 
     function hideReviewStep() {
-        reviewStep.hideAssessmentMessage();
-        gradeDOM.html('');
+        if (reviewStep) {
+            reviewStep.hideAssessmentMessage();
+            reviewStep.clearGrade(gradeDOM);
+        }
     }
 
     function getStepToReview(event) {

problem_builder/public/js/review_step.js

@@ -42,6 +42,10 @@ function ReviewStepBlock(runtime, element) {
 
             gradeDOM.html(gradeTemplate(data));
 
+        },
+
+        'clearGrade': function(gradeDOM) {
+            gradeDOM.html('');
         }
 
     };

problem_builder/tests/integration/test_step_builder.py

@@ -1251,3 +1251,12 @@ class StepBuilderTest(MentoringAssessmentBaseTest, MultipleSliderBlocksTestMixin
         # Clicking in general should dismiss this message.
         self.browser.execute_script("$(document).trigger('click')")
         self.wait_until_hidden(message)
+
+    def test_no_review_step(self):
+        step_builder, controls = self.load_assessment_scenario("step_builder_no_review_step.xml", {})
+        # If client-side code tries to call a method on reviewStep
+        # even if Step Builder block does not contain a review step,
+        # the current step will fail to render.
+        # In that case, submitting an answer and will fail,
+        # as it requires the corresponding question to be visible:
+        self.freeform_answer(None, step_builder, controls, 'This is the answer', CORRECT)

problem_builder/tests/integration/xml_templates/step_builder_no_review_step.xml

+<step-builder url_name="step-builder" display_name="Step Builder">
+
+  <sb-step display_name="First Step">
+    <pb-answer name="goal" question="What is your goal?" />
+  </sb-step>
+
+  <sb-step display_name="Second Step">
+    <pb-answer name="hobbies" question="What do you like to do for fun?" />
+  </sb-step>
+
+</step-builder>