Fix remove source branch link

app/helpers/merge_requests_helper.rb

@@ -181,4 +181,16 @@ module MergeRequestsHelper
   def different_base?(version1, version2)
     version1 && version2 && version1.base_commit_sha != version2.base_commit_sha
   end
+
+  def merge_params(merge_request)
+    {
+      merge_when_build_succeeds: true,
+      should_remove_source_branch: true,
+      sha: merge_request.diff_head_sha
+    }.merge(merge_params_ee(merge_request))
+  end
+
+  def merge_params_ee(merge_request)
+    { squash: merge_request.squash }
+  end
 end

app/views/projects/merge_requests/widget/open/_merge_when_build_succeeds.html.haml

@@ -24,7 +24,7 @@
   - if remove_source_branch_button || user_can_cancel_automatic_merge
     .clearfix.prepend-top-10
       - if remove_source_branch_button
-        = link_to merge_namespace_project_merge_request_path(@merge_request.target_project.namespace, @merge_request.target_project, @merge_request, merge_when_build_succeeds: true, should_remove_source_branch: true, sha: @merge_request.diff_head_sha), remote: true, method: :post, class: "btn btn-grouped btn-primary btn-sm remove_source_branch" do
+        = link_to merge_namespace_project_merge_request_path(@merge_request.target_project.namespace, @merge_request.target_project, @merge_request, merge_params(@merge_request)), remote: true, method: :post, class: "btn btn-grouped btn-primary btn-sm remove_source_branch" do
           = icon('times')
           Remove Source Branch When Merged