Null-Value in config results in ERROR RangeError: Maximum call stack size exceeded

[plusgut]

nightwatch.json:
{ "foobar": null }

Verbose:

ERROR RangeError: Maximum call stack size exceeded
    at Object.CliRunner.replaceEnvVariables (/Users/cjeske/tmp/nightwatch/lib/runner/cli/clirunner.js:111:33)
    at Object.CliRunner.replaceEnvVariables (/Users/cjeske/tmp/nightwatch/lib/runner/cli/clirunner.js:116:14)
    at Object.CliRunner.replaceEnvVariables (/Users/cjeske/tmp/nightwatch/lib/runner/cli/clirunner.js:116:14)
    at Object.CliRunner.replaceEnvVariables (/Users/cjeske/tmp/nightwatch/lib/runner/cli/clirunner.js:116:14)
    at Object.CliRunner.replaceEnvVariables (/Users/cjeske/tmp/nightwatch/lib/runner/cli/clirunner.js:116:14)
    at Object.CliRunner.replaceEnvVariables (/Users/cjeske/tmp/nightwatch/lib/runner/cli/clirunner.js:116:14)
    at Object.CliRunner.replaceEnvVariables (/Users/cjeske/tmp/nightwatch/lib/runner/cli/clirunner.js:116:14)
    at Object.CliRunner.replaceEnvVariables (/Users/cjeske/tmp/nightwatch/lib/runner/cli/clirunner.js:116:14)
    at Object.CliRunner.replaceEnvVariables (/Users/cjeske/tmp/nightwatch/lib/runner/cli/clirunner.js:116:14)
    at Object.CliRunner.replaceEnvVariables (/Users/cjeske/tmp/nightwatch/lib/runner/cli/clirunner.js:116:14)
There was an error while starting the test runner:

Error: No testing environment specified.
    at Object.CliRunner.parseTestSettings 
(/Users/cjeske/tmp/nightwatch/lib/runner/cli/clirunner.js:516:13)
    at Object.CliRunner.setup (/Users/cjeske/tmp/nightwatch/lib/runner/cli/clirunner.js:49:8)
    at Object.exports.runner (/Users/cjeske/tmp/nightwatch/lib/index.js:543:17)
    at /Users/cjeske/tmp/nightwatch/bin/runner.js:11:16
    at Object.exports.cli (/Users/cjeske/tmp/nightwatch/lib/index.js:537:5)
    at Object.<anonymous> (/Users/cjeske/tmp/nightwatch/bin/runner.js:9:14)
    at Module._compile (module.js:409:26)
    at Object.Module._extensions..js (module.js:416:10)
    at Module.load (module.js:343:32)
    at Function.Module._load (module.js:300:12)

When used this config:
{ "foobar": "" }

The result is correct:

There was an error while starting the test runner:

Error: No testing environment specified.
    at Object.CliRunner.parseTestSettings (/Users/cjeske/tmp/nightwatch/lib/runner/cli/clirunner.js:516:13)
    at Object.CliRunner.setup (/Users/cjeske/tmp/nightwatch/lib/runner/cli/clirunner.js:49:8)
    at Object.exports.runner (/Users/cjeske/tmp/nightwatch/lib/index.js:543:17)
    at /Users/cjeske/tmp/nightwatch/bin/runner.js:11:16
    at Object.exports.cli (/Users/cjeske/tmp/nightwatch/lib/index.js:537:5)
    at Object.<anonymous> (/Users/cjeske/tmp/nightwatch/bin/runner.js:9:14)
    at Module._compile (module.js:409:26)
    at Object.Module._extensions..js (module.js:416:10)
    at Module.load (module.js:343:32)
    at Function.Module._load (module.js:300:12)

The reason for all this is because typeof null === 'object'
and the recursive function in lib/runner/cli/clirunner.js:112 does a not typesecure check, if the given parameter is undefined.
Because of that, it starts over again and sets target to this.settings again. When iterating over it, it goes to the key foobar and it sees a object and calls itself with null and everything starts all over again.

Fixed in #1292