code: public void setBillingCap(com.google.api.ads.admanager.axis.v201811.BillingCap billingCap) {
          this.billingCap = billingCap;
      }
docs: Sets the billingCap value for this ProposalLineItem.
  
  @param billingCap   * Overrides the billing cap of this {@code ProposalLineItem}.
  This attribute is optional.
  
  If this field is overridden, then other required billing
  fields
  ({@link #billingSource}, or {@link #billingBase})
  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>