public static NoType asNoType(TypeMirror maybeNoType) {
    return maybeNoType.accept(NoTypeVisitor.INSTANCE, null);
  }
Returns a {@link NoType} if the {@link TypeMirror} represents an non-type such as void, or
package, etc. or throws an {@link IllegalArgumentException}.
common/src/main/java/com/google/auto/common/MoreTypes.java