public Builder port(@Nullable Integer port) {
      if (port != null) {
        if (port > 0xffff) throw new IllegalArgumentException("invalid port " + port);
        if (port <= 0) port = 0;
      }
      this.port = port != null ? port : 0;
      return this;
    }
Use this to set the port to an externally defined value.

@param port port associated with the endpoint. zero coerces to null (unknown)
@see Endpoint#port()
zipkin/src/main/java/zipkin2/Endpoint.java