code: public String getProperty(Key key) {
          final String envVariable = getPropertyFromEnvironment(key);
          if (envVariable != null) {
              return envVariable;
          }
          if (key.getDefaultValue() == null) {
              return properties.getProperty(key.getPropertyName());
          } else {
              return properties.getProperty(key.getPropertyName(), String.valueOf(key.getDefaultValue()));
          }
      }
docs: Return the configured value for the specified Key. As of v1.4.3, this
  method will first check if the key has been specified as an environment
  variable. If it has, the method will return the value. If it hasn't
  been specified in the environment, it will retrieve the value (and optional
  default value) from the properties configuration.
  
  This method is Docker-friendly in that configuration can be specified via
  environment variables which is a common method of configuration when
  configuration files are not easily accessible.
  
  @param key The Key to return the configuration for
  @return a String of the value of the configuration
  @since 1.0.0