private boolean isUnresolvableTypeVariable() {
        if (this.type instanceof TypeVariable) {
            if (this.variableResolver == null) {
                return true;
            }
            TypeVariable<?> variable = (TypeVariable<?>) this.type;
            ResolvableType resolveD = this.variableResolver.resolveVariable(variable);
            return resolveD == null || resolveD.isUnresolvableTypeVariable();
        }
        return false;
    }
Determine whether the underlying type is a type variable that
cannot be resolved through the associated variable resolver.
analyzer/src/main/java/nl/basjes/parse/useragent/utils/springframework/core/ResolvableType.java