private static Type parameterizedTypeOf(AnnotatedElement element) {
        if (element instanceof Parameter) {
            return ((Parameter) element).getParameterizedType();
        }
        if (element instanceof Field) {
            return ((Field) element).getGenericType();
        }
        throw new IllegalArgumentException("Unsupported annotated element: " +
                                           element.getClass().getSimpleName());
    }
Returns an attribute resolver which retrieves a value specified by {@code attrKeys}
from the {@link RequestContext}.
core/src/main/java/com/linecorp/armeria/internal/server/annotation/AnnotatedValueResolver.java