[1.0.x] Custom commands that use execute and are called with page-object elements throw an error

[aberonni]

On our codebase we make extensive use of this sort of setup:

// myPage.js
elements: {
    myElement: '#mySelector'
}

// myCustomCommand.js
exports.command = function(selector) {
    this.execute(
        function(data) {
             // execute application specific code
            return 'something';
        },
        [selector],
        function(result) {
             // do something with result
        }
    );
    return this;
};

// test
const page = browser.page.myPage()

page.myCustomCommand('@myElement')

This worked as expected with Nightwatch < 1, but with latest version it breaks, so it seems like a regression.

Nightwatch version: 1.0.11
Node version: 10.8.0
OS: MacOS 10.13.6
Selenium: 3.13.0

Error output:

   Converting circular structure to JSON
       at JSON.stringify (<anonymous>)
       at Function.jsonStringify (/Users/dom/git/nightwatch/lib/http/formatter.js:15:23)
       at HttpRequest.setOptions (/Users/dom/git/nightwatch/lib/http/request.js:69:43)
       at new HttpRequest (/Users/dom/git/nightwatch/lib/http/request.js:34:10)
       at JsonWireProtocol.createProtocolAction (/Users/dom/git/nightwatch/lib/transport/transport.js:184:21)
       at JsonWireProtocol.runProtocolAction (/Users/dom/git/nightwatch/lib/transport/jsonwire.js:49:24)
       at target.(anonymous function).definition (/Users/dom/git/nightwatch/lib/transport/actions.js:46:33)
       at Proxy.<anonymous> (/Users/dom/git/nightwatch/lib/api/protocol.js:70:18)
       at ProtocolActions.executeScriptHandler (/Users/dom/git/nightwatch/lib/api/protocol.js:1445:41)
       at ProtocolActions.execute (/Users/dom/git/nightwatch/lib/api/protocol.js:1071:21)
 Error while running .executeScript() protocol action: unknown error: 'script' must be a string

{ status: -1,
  state: '',
  value:
   { message: 'unknown error: \'script\' must be a string',
     error:
      [ '  (Session info: chrome=69.0.3497.100)',
        '  (Driver info: chromedriver=2.41.578706 (5f725d1b4f0a4acbf5259df887244095596231db),platform=Mac OS X 10.13.4 x86_64)'] },
  errorStatus: 13,
  error: 'unknown error: \'script\' must be a string',
  httpStatusCode: 200 }
No assertions ran.

You can reproduce here: https://github.com/aberonni/nightwatch-bug-report/tree/master/tests/1882

npm install
npm run test:1882

[aberonni]

@beatfactor closing in favour of #1237 - could you add the v1.0 label to that issue?