How can I avoid this issue?

[navisoft]

public function getModel(className, args = null) {
    if class_exists("App\\" . className) {
        echo "E";
        var_dump(className);
        let className = "App\\" . className;
    } else {
        echo "N";
        var_dump(className);
        let className = "Default\\" . className;
    }
    return new {className}(args);
}

I have the class "App\Product" and when I use the function getModel("Product"), it's error. After check class_exists("App\" . className), the variable className becomes null and then the final className is "App\" and it causes issue.

[Jeckerson]

Try to use separate variable for full class name with namespace:

string class;

if class_exists() {
    let class = "App\\" . className;
} else {
    let class = "Default\\" . className;
}