Update capture to handle empty blocks

sinatra-contrib/lib/sinatra/capture.rb

@@ -110,7 +110,7 @@ def capture(*args, &block)
         buffer.clear unless buffer.nil?
         result = render(current_engine, dummy, options, &block)
       end
-      result.strip.empty? && @capture ? @capture : result
+      result && result.strip.empty? && @capture ? @capture : result
     ensure
       buffer.replace(old_buffer) unless buffer.nil?
     end

sinatra-contrib/spec/capture_spec.rb

@@ -50,6 +50,12 @@ def render(engine, template)
       expect(render(:erb, "iso_8859_1")).to eq("ISO-8859-1 -")
     end
   end
+
+  describe 'without templates' do
+    it 'captures empty blocks' do
+      expect(capture {}).to be_nil
+    end
+  end
 end
 
 __END__

sinatra-contrib/spec/content_for_spec.rb

@@ -33,7 +33,7 @@ def render(engine, template)
     end
 
     it 'renders default content if no block matches the key and a default block is specified' do
-      content_for(:bar) { "bar" }
+      expect(yield_content(:foo) {}).to be_nil
       expect(yield_content(:foo) { "foo" }).to eq("foo")
     end