code: public DirectConnectGatewayAssociationProposal withExistingAllowedPrefixesToDirectConnectGateway(
              RouteFilterPrefix... existingAllowedPrefixesToDirectConnectGateway) {
          if (this.existingAllowedPrefixesToDirectConnectGateway == null) {
              setExistingAllowedPrefixesToDirectConnectGateway(new com.amazonaws.internal.SdkInternalList<RouteFilterPrefix>(
                      existingAllowedPrefixesToDirectConnectGateway.length));
          }
          for (RouteFilterPrefix ele : existingAllowedPrefixesToDirectConnectGateway) {
              this.existingAllowedPrefixesToDirectConnectGateway.add(ele);
          }
          return this;
      }
docs: <p>
  The existing Amazon VPC prefixes advertised to the Direct Connect gateway.
  </p>
  <p>
  <b>NOTE:</b> This method appends the values to the existing list (if any). Use
  {@link #setExistingAllowedPrefixesToDirectConnectGateway(java.util.Collection)} or
  {@link #withExistingAllowedPrefixesToDirectConnectGateway(java.util.Collection)} if you want to override the
  existing values.
  </p>
  
  @param existingAllowedPrefixesToDirectConnectGateway
  The existing Amazon VPC prefixes advertised to the Direct Connect gateway.
  @return Returns a reference to this object so that method calls can be chained together.