avoid posting empty comments

fix Jasmine test

updated changelog with bugfix #3836

fix changelog update

remove wrong bug fix line

Changelog.md

 # Head
 
+## Bug fixes
+
+* avoid posting empty comments. [#3836](https://github.com/diaspora/diaspora/issues/3836)
+
 ## Refactor
 
 * Refactor people_controller#show and photos_controller#index [#4002](https://github.com/diaspora/diaspora/issues/4002)
@@ -57,7 +61,7 @@
 * Stream form on profile page [#3910](https://github.com/diaspora/diaspora/issues/3910).
 * Add Getting_Started page mobile. [#3949](https://github.com/diaspora/diaspora/issues/3949).
 * Autoscroll to the first unread message in conversations. [#3216](https://github.com/diaspora/diaspora/issues/3216)
-* Friendlier new-conversation mobile. [#3984](https://github.com/diaspora/diaspora/issues/3984) 
+* Friendlier new-conversation mobile. [#3984](https://github.com/diaspora/diaspora/issues/3984)
 
 ## Bug Fixes
 

app/assets/javascripts/app/views/comment_stream_view.js

@@ -39,9 +39,15 @@ app.views.CommentStream = app.views.Base.extend({
 
   createComment: function(evt) {
     if(evt){ evt.preventDefault(); }
-    this.model.comment(this.$(".comment_box").val())
-    this.$(".comment_box").val("")
-    return this;
+    
+    var commentText = $.trim(this.$('.comment_box').val());
+    if(commentText) {
+      this.model.comment(commentText);
+      this.$(".comment_box").val("");
+      return this;
+    } else {
+      this.$(".comment_box").val("").focus();
+    }
   },
 
   appendComment: function(comment) {

spec/javascripts/app/views/comment_stream_view_spec.js

@@ -28,6 +28,26 @@ describe("app.views.CommentStream", function(){
       expect($.fn.autoResize.mostRecentCall.object.selector).toBe("textarea")
     })
   })
+  
+  describe("createComment", function() {
+    beforeEach(function() {
+      jasmine.Ajax.useMock();
+      this.view.render();
+      this.view.expandComments();
+    })
+    
+    it("submits the new comment when comment text is not empty", function() {
+      this.view.$(".comment_box").val('a new comment');
+      this.view.createComment();
+      expect(this.view.$(".comment-content p").text()).toEqual("a new comment");
+    })
+    
+    it("clears the comment box when there are only spaces", function() {
+      this.view.$(".comment_box").val('   ');
+      this.view.createComment();
+      expect(this.view.$(".comment_box").val()).toEqual("");
+    })
+  })
 
   describe("appendComment", function(){
     it("appends this.model as 'parent' to the comment", function(){