code: public void setOperation(com.google.api.ads.adwords.axis.v201809.o.LongComparisonOperation operation) {
          this.operation = operation;
      }
docs: Sets the operation value for this SearchVolumeSearchParameter.
  
  @param operation   * Used to specify the range of search volume.
  <span class="constraint Required">This field is
  required and should not be {@code null}.</span>