Fix issue with params in url_for

With a "params" argument, the following error is raised:

    undefined method `reject!` for "":String

Author: tumayun

actionpack/lib/action_dispatch/http/url.rb

@@ -28,7 +28,7 @@ def url_for(options = {})
           path  = options.delete(:script_name).to_s.chomp("/")
           path << options.delete(:path).to_s
 
-          params = options[:params] || {}
+          params = options[:params].is_a?(Hash) ? options[:params] : {}
           params.reject! { |_,v| v.to_param.nil? }
 
           result = build_host_url(options)

actionpack/test/dispatch/request_test.rb

@@ -799,6 +799,14 @@ def url_for(options = {})
     end
   end
 
+  test "url_for options[:params]" do
+    assert_equal 'http://www.example.com?params=', url_for(:params => '')
+    assert_equal 'http://www.example.com?params=1', url_for(:params => 1)
+    assert_equal 'http://www.example.com', url_for
+    assert_equal 'http://www.example.com', url_for(:params => {})
+    assert_equal 'http://www.example.com?name=tumayun', url_for(:params => { :name => 'tumayun' })
+  end
+
 protected
 
   def stub_request(env = {})