Allow domainLockRedirectUrl to accept empty string

[xenovation]

Is your feature request related to a problem? Please describe.

I believe there is some bug with domainlock under certain circumstance, it was difficult to reproduce because it happens rarely.

Describe the solution you'd like

Can we please allow this option to accept empty string, so that the code will just stop working but not redirect? I believe many users do not need redirect as well, for me the important function for this option is to just stop the code from working if the script was run not on my domains.