Entity#serializable_hash works when nil is passed in. Closes ruby-grape#71

Author: Michael Bleigh

lib/grape/entity.rb

@@ -118,7 +118,7 @@ def exposures
     #   representation, this is where you can trigger things from conditional options
     #   etc.
     def serializable_hash(runtime_options = {})
-      opts = options.merge(runtime_options)
+      opts = options.merge(runtime_options || {})
       exposures.inject({}) do |output, (attribute, exposure_options)|
         output[key_for(attribute)] = value_for(attribute, opts) if conditions_met?(exposure_options, opts)
         output

spec/grape/entity_spec.rb

@@ -87,6 +87,9 @@
     subject{ fresh_class.new(model) }
 
     describe '#serializable_hash' do
+      it 'should not throw an exception if a nil options object is passed' do
+        expect{ fresh_class.new(model).serializable_hash(nil) }.not_to raise_error
+      end
     end
 
     describe '#value_for' do