What's wrong with this script?

This opens a project in RoboHTML:

var projectPath = "C:\\scratch\\test\\test.xpj";

main();

function main()

{

RoboHelp.openProject(projectPath);

}

This opens RoboHTML but not the project:

var projectPath = "C:\\scratch\\test\\test.xpj";

main();

function main()

{

        if(projectPath = '')

        {

               alert("Project path is not defined. \nPlease update the 'projectPath' variable in the script.");

               RoboHelp.quit();

        }

        RoboHelp.openProject(projectPath);

}

What's the error?