code: public Mono<HttpResponse> process() {
          final int size = this.pipeline.pipelinePolicies().length;
          if (this.currentPolicyIndex > size) {
              return Mono.error(new IllegalStateException("There is no more policies to execute."));
          } else {
              this.currentPolicyIndex++;
              if (this.currentPolicyIndex == size) {
                  return this.pipeline.httpClient().send(this.context.httpRequest());
              } else {
                  return this.pipeline.pipelinePolicies()[this.currentPolicyIndex].process(this.context, this);
              }
          }
      }
docs: Invokes the next {@link HttpPipelinePolicy}.
  
  @return a publisher upon subscription invokes next policy and emits response from the policy.