fixes assignment creation with quick add dialog

fixes CNVS-15217

test plan
- create an ungraded assignment using the quick add dialog
- do it again using the 'quiz' or 'discussion' type
- do it again and click 'more options'
- save the assignment with a single online submission option
- verify that it saves/works for every assignment you created
- party party celebrate victory wooo 👍

Change-Id: Ib4c924801d3f3ed228971151d88c97b7bc572fb1
Reviewed-on: https://gerrit.instructure.com/40416
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cameron Sutter <csutter@instructure.com>
QA-Review: Amber Taniuchi <amber@instructure.com>
Product-Review: Liz Abinante <labinante@instructure.com>

Author: slothelle

lib/api/v1/assignment.rb

@@ -296,20 +296,12 @@ def update_api_assignment(assignment, assignment_params, user)
     return false
   end
 
-  API_ALLOWED_SUBMISSION_TYPES = %w(
-    online_quiz
-    none
-    on_paper
-    discussion_topic
-    external_tool
-    online_upload
-    online_text_entry
-    online_url
-    media_recording
-    not_graded
-  )
+  API_ALLOWED_SUBMISSION_TYPES = ["online_quiz", "none", "on_paper", "discussion_topic", "external_tool", "online_upload", "online_text_entry", "online_url", "media_recording", "not_graded", ""]
 
   def valid_submission_types?(assignment, assignment_params)
+    return true if assignment_params['submission_types'].nil?
+    assignment_params['submission_types'] = Array(assignment_params['submission_types'])
+
     if assignment_params['submission_types'].present? &&
       !assignment_params['submission_types'].all? { |s| API_ALLOWED_SUBMISSION_TYPES.include?(s) }
         assignment.errors.add('assignment[submission_types]',

spec/apis/v1/assignments_api_spec.rb

@@ -578,7 +578,7 @@ def create_assignment_json(group, group_category)
       end
     end
 
-    it "should allow valid submission types" do
+    it "should allow valid submission types as an array" do
       raw_api_call(:post, "/api/v1/courses/#{@course.id}/assignments",
         { :controller => 'assignments_api',
           :action => 'create',
@@ -594,6 +594,19 @@ def create_assignment_json(group, group_category)
       response.should be_success
     end
 
+    it "should allow valid submission types as a string (quick add dialog)" do
+      raw_api_call(:post, "/api/v1/courses/#{@course.id}/assignments",
+        { :controller => 'assignments_api',
+          :action => 'create',
+          :format => 'json',
+          :course_id => @course.id.to_s },
+        { :assignment => {
+            'name' => 'some assignment',
+            'submission_types' => 'not_graded'}
+      })
+      response.should be_success
+    end
+
     it "should not allow unpermitted submission types" do
       raw_api_call(:post, "/api/v1/courses/#{@course.id}/assignments",
         { :controller => 'assignments_api',