Enforce saving content_type as a string with test

lib/paperclip/attachment.rb

@@ -95,7 +95,7 @@ module Paperclip
 
       @queued_for_write[:original]   = file
       instance_write(:file_name,       cleanup_filename(file.original_filename))
-      instance_write(:content_type,    file.content_type)
+      instance_write(:content_type,    file.content_type.to_s.strip)
       instance_write(:file_size,       file.size)
       instance_write(:fingerprint,     file.fingerprint) if instance_respond_to?(:fingerprint)
       instance_write(:updated_at,      Time.now)

lib/paperclip/io_adapters/stringio_adapter.rb

@@ -16,7 +16,7 @@ module Paperclip
     def content_type
       @content_type ||= @target.content_type if @target.respond_to?(:content_type)
       @content_type ||= "text/plain"
-      @content_type.strip
+      @content_type
     end
 
     def size

test/attachment_test.rb

@@ -691,6 +691,21 @@ class AttachmentTest < Test::Unit::TestCase
     end
   end
 
+  context "Assigning an attachment" do
+    setup do
+      rebuild_model :styles => { :something => "100x100#" }
+      @file = StringIO.new(".")
+      @file.stubs(:original_filename).returns("5k.png\n\n")
+      @file.stubs(:content_type).returns(MIME::Type.new("image/png"))
+      @dummy = Dummy.new
+      @dummy.avatar = @file
+    end
+
+    should "make sure the content_type is a string" do
+      assert_equal "image/png", @dummy.avatar.instance.avatar_content_type
+    end
+  end
+
   context "Attachment with strange letters" do
     setup do
       rebuild_model