Merge pull request #2107 from edx/anton/fix-image-response

Fix show answer button for ImageResponse.

common/lib/xmodule/xmodule/js/spec/capa/display_spec.coffee

@@ -308,11 +308,17 @@ describe 'Problem', ->
         states = [
           {
             desc: 'rectangle is drawn correctly',
-            data: {'rectangle': '(10,10)-(30,30)'}
+            data: {
+              'rectangle': '(10,10)-(30,30)',
+              'regions': null
+            }
           },
           {
             desc: 'region is drawn correctly',
-            data: {'regions': '[[10,10],[30,30],[70,30],[20,30]]'}
+            data: {
+              'rectangle': null,
+              'regions': '[[10,10],[30,30],[70,30],[20,30]]'
+            }
           },
           {
             desc: 'mixed shapes are drawn correctly',
@@ -387,7 +393,7 @@ describe 'Problem', ->
           ctx.lineWidth = "2";
 
           $.each coords, (key, value) =>
-            types[key](value) if types[key]?
+            types[key](value) if types[key]? and value
 
           return canvas
 

common/lib/xmodule/xmodule/js/src/capa/display.coffee

@@ -260,7 +260,7 @@ class @Problem
 
   check: =>
     if not @check_save_waitfor(@check_internal)
-      @check_internal()  
+      @check_internal()
 
   check_internal: =>
     Logger.log 'problem_check', @answers
@@ -570,7 +570,7 @@ class @Problem
 
       $.each answers, (key, answer) =>
         $.each answer, (key, value) =>
-          types[key](value) if types[key]?
+          types[key](value) if types[key]? and value
 
       container.html(canvas)