Lookup fields and null question help

Lookup fields and null question help

So I have application Test

I have a lookup field Lookup_11

With fields for customer email, phone number ect

how do I make this code allow reservations even when some of the fields are not filled out or have a different email or ect that is not in the Registrations table? I keep getting null error messages when I submit the form.

rec  =  Registrations  [First_Last_Name == input.Lookup_11];
Email=rec.Email_1;
input.First_Name = rec.First_Name;
input.Last_Name = rec.Last_Name;
input.Phone_number = rec.Phone_Number;

for now I am having to comment out this code
but it would be great if the customer can look up their name or leave the fields blank

Thanks!