message: core: don't call std::string(NULL)
diff: @@ -1655,12 +1655,7 @@ cv::String utils::getConfigurationParameterString(const char* name, const char*
  #else
  const char* envValue = getenv(name);
  #endif
  - if (envValue == NULL)
  - {
  - return defaultValue;
  - }
  - cv::String value = envValue;
  - return value;
  + return envValue ? cv::String(envValue) : (defaultValue ? cv::String(defaultValue) : cv::String());
  }
  