code: static TypeMirror getAdaptedType(Elements elements, Types types, DeclaredType adapterType) {
      TypeElement typeAdapterElement = elements.getTypeElement(TYPE_ADAPTER_CLASS_NAME);
      TypeParameterElement param = typeAdapterElement.getTypeParameters().get(0);
      return paramAsMemberOf(types, adapterType, param);
    }
docs: Returns the {@link TypeMirror} argument found in a given {@code TypeAdapter} type.