What does the question mark mean in GSP/Grails?

Question

I saw this in my generated GSP pages. What does the ? mean?

Answer 1

The ? operator allows null values in Groovy (and thusly, GSP). For example, normally in gsp,

If priceDetails is null, this will throw a NullPointerException.

If we use the ? operator instead ...

now the value of ${priceDetails?.amount} is null, instead of throwing a null pointer exception.