How can I set initial password for metarunner or set it empty

I've created a build-conf with password param. When I edit parameter and set it's constrains to "Password field" every time I save it replaces my password from field "Value" to %secure:teamcity.password.testrunner.password%. Ok, my build-conf works well.

But when I  export it to meta-runner I see something like this in XML 

 <param name="testrunner.password" value="zxx202de374f5a496dd780bd19bd670dd1c"

and then I try to use this meta-runner and instead of password string in my script I get "%secure:teamcity.testrunner.moveagent.password%" .

I'd like that either I can set default password for meta-runner or set it required and empty. How can I do this?