dart - What does the exclamation mark mean before a function call?

Question

I was following a PR for Flutter and came across this code:

if (chunkCallback != null) {
  chunkCallback!(0, 100);
}

What does the exclamation mark mean after chunkCallback? Nothing I search on Google works.

Answer 1

"!" is a new dart operator for conversion from a nullable to a non-nullable type. Read here and here about sound null safety.

Use it only if you are absolutely sure that the value will never be null and do not confuse it with the conditional property access operator.