Knock Knock joke

Holland absolutely LOVES Johnny Cash and June Carter! She has these princess plastic shoes but they aren't princess shoes they are June Carter shoes!! She knows the songs and sings them all the time, it's really cute. She has a knock knock joke that she likes to do..
"Knock Knock"
"Who's there?"
"Johnny Cash"
"Johnny Cash who?"
"JUNE CARTER!!!"
then she laughs really hard!
Yeah, it doesn't makes sense, but she's 3 and it's so cute!!