code: @JsonIgnore
      public void validate() throws OpsGenieClientValidationException {
          if (apiKey == null)
              throw OpsGenieClientValidationException.missingMandatoryProperty(OpsGenieClientConstants.API.API_KEY);
      }
docs: check the parameters for validation. It will be overridden by necessary
  Requests.
  
  @throws OpsGenieClientValidationException when api key is null!