What means the undefined "method" in "IncomingMessage" of "http" module?

According TypeScript types definitions, the "IncomingMessage.method" could be undefined:

class IncomingMessage extends stream.Readable {
  // ...
  method?: string | undefined;
}

What the undefined value tells to us and how me should handle this value?

Currently I do it as below:

import HTTP from "http";
import {
  HTTP_StatusCodes,
  Logger,
  isUndefined,
  UnsupportedScenarioError
} from "@yamato-daiwa/es-extensions";


class Server {

  private async requestMasterListener(
    request: HTTP.IncomingMessage,
    rawResponse: HTTP.ServerResponse,
    loggingData: {
      port: number;
      protocol: string;
    }
  ): Promise<void> {

    // ...

    if (isUndefined(request.method)) {
      Logger.logError({
        errorType: UnsupportedScenarioError.NAME,
        title: UnsupportedScenarioError.DEFAULT_TITLE,
        description: "The HTTP method is not defined.",
        occurrenceLocation: "Server.requestMasterListener(request, rawResponse)"
      });
      rawResponse.
          writeHead(HTTP_StatusCodes.badRequest, "HTTP method is not specified").
          end();
      return;
    }

    // ...
  }
}