Allow Strings as well as Symbols as #permit parameters. Useful

when persisting multi-purpose String arrays to the #permit
call.

lib/action_controller/parameters.rb

@@ -37,7 +37,7 @@ def permit(*filters)
 
       filters.each do |filter|
         case filter
-        when Symbol then
+        when Symbol, String then
           params[filter] = self[filter] if has_key?(filter)
         when Hash then
           self.slice(*filter.keys).each do |key, value|

test/nested_parameters_test.rb

@@ -43,6 +43,21 @@ class NestedParametersTest < ActiveSupport::TestCase
     assert_equal ["Tragedy"], permitted[:book][:genres]
   end
 
+  test "permit may specify symbols or strings" do
+    params = ActionController::Parameters.new({
+      book: {
+        title: "Romeo and Juliet",
+        author: "William Shakespeare"
+      },
+      magazine: "Shakespeare Today"
+    })
+
+    permitted = params.permit({book: ["title", :author]}, "magazine")
+    assert_equal "Romeo and Juliet", permitted[:book][:title]
+    assert_equal "William Shakespeare", permitted[:book][:author]
+    assert_equal "Shakespeare Today", permitted[:magazine]
+  end
+
   test "nested array with strings that should be hashes" do
     params = ActionController::Parameters.new({
       book: {