code: public ServiceFuture<VirtualWANInner> beginCreateOrUpdateAsync(String resourceGroupName, String virtualWANName, VirtualWANInner wANParameters, final ServiceCallback<VirtualWANInner> serviceCallback) {
          return ServiceFuture.fromResponse(beginCreateOrUpdateWithServiceResponseAsync(resourceGroupName, virtualWANName, wANParameters), serviceCallback);
      }
docs: Creates a VirtualWAN resource if it doesn't exist else updates the existing VirtualWAN.
  
  @param resourceGroupName The resource group name of the VirtualWan.
  @param virtualWANName The name of the VirtualWAN being created or updated.
  @param wANParameters Parameters supplied to create or update VirtualWAN.
  @param serviceCallback the async ServiceCallback to handle successful and failed responses.
  @throws IllegalArgumentException thrown if parameters fail the validation
  @return the {@link ServiceFuture} object