boolean hasContainer() {
        return containerType != null &&
               (List.class.isAssignableFrom(containerType) || Set.class.isAssignableFrom(containerType));
    }
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