message: fix crash for responses without content but with headers
diff: @@ -39,7 +39,7 @@ export class ResponseView extends React.Component<{ response: ResponseModel }> {
  <ResponseDetailsWrap>
  <ResponseHeaders headers={headers} />
  <MediaTypesSwitch
  - content={content!}
  + content={content}
  renderDropdown={props => (
  <UnderlinedHeader key="header">
  Response Schema: <DropdownOrLabel {...props} />
  