Fix 'yield outside of switch expression'

[alsin]

When using Immutables with Java versions supporting switch expressions (and the new yield keyword) and if one decides to define an immutable interface with say getYield() method:

@Value.Immutable
public interface SomeInterface {
    int getYield();
}

the value processor generates an immutable class implementation which won't compile since the internal generated Builder class would have the following copying method:

    @CanIgnoreReturnValue 
    public final Builder from(SomeInterface instance) {
      Objects.requireNonNull(instance, "instance");
      yield(instance.getYield()); <-- here the compiler will fail with 'Yield outside of switch expression'
      return this;
    }

It's enough to prepend the method call with this. and the compilation passes.

[elucash]

Thank you for the PR, I wonder if there are other places affected.

[alsin]

Thank you for the PR, I wonder if there are other places affected.

You're welcome! Could be, I just came across this bug on this particular place. Had to fix it temporarily by changing the setter style (using set*).