Configuration.port should be a number

When initialising webpack-dev-server 2.2.0 I get the following error:

Invalid configuration object. webpack-dev-server has been initialised using a configuration object that does not match the API schema.
 - configuration.port should be a number.
error Command failed with exit code 1.

I'm reading the port from an environment variable (with the contents 8080). Using port: parseInt(process.env.DEV_PORT) (here) solves the problem, but I was just wondering if this is meant to work like this, as I have no way to influence whether the environment variable reads as a string or a number, other than using parseInt.

[SpaceK33z]

I'm not completely sure about this. Technically an integer is the most correct form, but an integer also works. parseInt() is the way to go, at least for now.