public static WildcardType asWildcard(TypeMirror maybeWildcardType) {
    return maybeWildcardType.accept(WildcardTypeVisitor.INSTANCE, null);
  }
Returns a {@link WildcardType} if the {@link TypeMirror} represents a wildcard type or throws
an {@link IllegalArgumentException}.
common/src/main/java/com/google/auto/common/MoreTypes.java