valFn = function (v, ctx) {
            if (typeof v === "string") {
                if (ctx && ctx.allowEmptyStrings) return true;
                return v.length > 0;
            } else {
                return v != null;
            }
        }
Returns a standard 'required value' Validator
    @example
        // Assume em1 is a preexisting EntityManager.
        var custType = em1.metadataStore.getEntityType("Customer");
        var regionProperty - custType.getProperty("Region");
        // Makes "Region" on Customer a required property.
        regionProperty.validators.push(Validator.required());
    @method required
    @static
    @return {Validator} A new Validator