Fixing the "Token undefined not a primary expression at column null of the expression" error

The other day I was working on an Angular application and I received the following error message:

Token ‘undefined’ not a primary expression at column null of the expression

This was not a very helpful error message but I tracked it down to the following:

<label ng-click=toggleIsRequiredChecked($event, activeModules, module)">
    <input type="checkbox" ng-checked="getIsRequiredChecked(activeModules, moduleName)">
    
</label>

Do you see the error? The double quote is missing from the ng-click attribute which caused the error. I added it and the code worked:

<label ng-click="toggleIsRequiredChecked($event, activeModules, module)">
    <input type="checkbox" ng-checked="getIsRequiredChecked(activeModules, moduleName)">
    
</label>