In new tab create method I see that all Parameters for createProperties(object) are marked "optional". But when I try 
//if there is no storage create a new tab
var firstRun = (localStorage['firstRun'] == 'true') ;
if (!firstRun)
{
    chrome.tabs.create() 
    {
        console.log("new tab is created")   
    }
}
I get Uncaught Error: Parameter 1 is required.. This answer to a similar question also appears to say that parameters are optional.
What am I missing? Thanks.