message: BufferBody: check buffer for nullptr.
diff: namespace oatpp { namespace web { namespace protocol { namespace http { namespace outgoing {
  BufferBody::BufferBody(const oatpp::String &buffer, const data::share::StringKeyLabel &contentType)
  - : m_buffer(buffer)
  + : m_buffer(buffer ? buffer : "")
  , m_contentType(contentType)
  , m_inlineData((void*) m_buffer->data(), m_buffer->size())
  {}
  