Buffer with no url returns Text as its mode.

spec/atom/buffer-spec.coffee

@@ -51,7 +51,10 @@ describe 'Buffer', ->
         buffer = new Buffer 'something.js'
         expect(buffer.getMode().name).toBe 'javascript'
 
-    describe "when no url is given", ->
-      it "sets 'mode' to text mode", ->
         buffer = new Buffer 'something'
         expect(buffer.getMode().name).toBe 'text'
+
+    describe "when no url is given", ->
+      it "sets 'mode' to text mode", ->
+        buffer = new Buffer null
+        expect(buffer.getMode().name).toBe 'text'

src/atom/buffer.coffee

@@ -23,7 +23,7 @@ class Buffer
   getMode: ->
     return @mode if @mode
 
-    extension = @url.split('/').pop().split('.').pop()
+    extension = if @url then @url.split('/').pop().split('.').pop() else null
     modeName = switch extension
       when "js" then "javascript"
       else "text"