Merge pull request #19 from github/no-block

Make initialize without block return `true` for `ok?`

lib/github/result.rb

@@ -15,7 +15,7 @@ module GitHub
     #
     def initialize
       begin
-        @value = yield
+        @value = yield if block_given?
         @error = nil
       rescue => e
         @error = e

test/github/result_test.rb

@@ -83,4 +83,8 @@ class GitHub::ResultTest < Minitest::Test
 
     assert_equal e, GitHub::Result.new { raise e }.error
   end
+
+  def test_initialize_without_block
+    assert_predicate GitHub::Result.new, :ok?
+  end
 end