code: public void setBillingBase(com.google.api.ads.admanager.axis.v201902.BillingBase billingBase) {
          this.billingBase = billingBase;
      }
docs: Sets the billingBase value for this ProposalLineItem.
  
  @param billingBase   * Overrides the billing base of this {@code ProposalLineItem}.
  This attribute is optional.
  
  <p>If this field is overridden, then other required
  billing fields ({@link #billingCap}, {@link
  #billingSchedule}, or {@link #billingSource}) also
  need to be overridden depending on the
  {@link #billingSource}. That is, none of the billing
  fields will inherit from their {@link
  Proposal} object anymore. This attribute can be configured
  as editable after the proposal has
  been submitted. Please check with your network administrator
  for editable fields configuration.
  <span class="constraint Applicable">This attribute
  is applicable when:<ul><li>not using programmatic, using sales management.</li></ul></span>