code: public com.google.api.ads.adwords.axis.v201809.cm.Criterion getCriterion() {
          return criterion;
      }
docs: Gets the criterion value for this AdGroupBidModifier.
  
  @return criterion   * The criterion whose bid value is being overridden.
  
  <p>Currently, bid modifier overrides are supported
  only for platform criterion
  (ID=30000, 30001, 30002) and preferred content criterion
  (ID = 400).
  The {@linkplain AdGroupBidModifierService#get} method
  returns all platform and
  preferred content criteria.
  <span class="constraint Required">This field is required
  and should not be {@code null}.</span>