@Julenaworld 

the default is {{ first_name|default:''|capfirst }} which will take persons name from your account and use it instead.. but in case the subscriber doesn’t have a name in your klaviyo account you can use some word to use that instead if the name is not available.. 

People usually use Customer or Friend or something like that.. and the code for that is simple for example {{ first_name|default:'Friend'|capfirst }}.. whatever you like the word to be just add it between '' in the code.. so in this case.. if subscriber has a name this code will use their name and if they don’t have the name it will say Hi Friend instead..

I was searching today for an answer to this and ran across this thread from 2 years ago. I’m used to Mailchimp so forgive me. If I understand your explanation here, every time I want the empty first name field to default to Friend, I have to write this code? Isn’t there a permanent place in settings I can enter this? If the profile doesn’t have a first name, I want it to ALWAYS default to Friend. Are you saying I have to enter this code each and every time I use the first name merge tag? Also, is the capfirst part essential? Thanks for your help, Bobi.

@Jennifer H 

You can watch this video I made on YouTube about this exact thing a while ago..