code: public TypeElement getGenericType(TypeMirror typeMirror) {
          return typeMirror.accept(new SimpleTypeVisitor6<TypeElement, Void>() {
              @Override
              public TypeElement visitDeclared(DeclaredType declaredType, Void v) {
                  TypeElement genericTypeElement = null;
                  TypeElement typeElement = (TypeElement) declaredType.asElement();
                  if (parcelClass != null && typeUtils.isAssignable(typeElement.asType(), listTypeMirror)) {
                      List<? extends TypeMirror> typeArguments = declaredType.getTypeArguments();
                      if (!typeArguments.isEmpty()) {
                          for (TypeMirror genericType : typeArguments) {
                              if (genericType instanceof WildcardType) {
                                  WildcardType wildcardType = (WildcardType) genericType;
                                  TypeMirror extendsType = wildcardType.getExtendsBound();
                                  if (extendsType != null) {
                                      typeElement = elementUtils.getTypeElement(extendsType.toString());
                                      if (typeElement.getAnnotation(parcelClass) != null) {
                                          genericTypeElement = typeElement;
                                          break;
                                      }
  
                                  }
                              } else {
                                  typeElement = elementUtils.getTypeElement(genericType.toString());
                                  if (typeElement.getAnnotation(parcelClass) != null) {
                                      genericTypeElement = typeElement;
                                      break;
                                  }
                              }
                          }
                      }
                  }
                  return genericTypeElement;
              }
          }, null);
      }
docs: Return the generic type if any