Compiling code like this:

var _ = someExpression();

Results in this report from Error Prone (2.28.0):

java: [UnusedVariable] The local variable '' is never read.
    (see https://errorprone.info/bugpattern/UnusedVariable)
  Did you mean to remove this line?

This is a new feature in Java 22, which can be used to deliberately ignore a return value e.g. from methods declared as "must use return value". Note that the UnusedVariable check works fine in this case if the variable is called "ignored" or something like that.