static _propertyValueToAttribute(value, options) {
        if (options.reflect === undefined) {
            return;
        }
        const type = options.type;
        const converter = options.converter;
        const toAttribute = converter && converter.toAttribute ||
            defaultConverter.toAttribute;
        return toAttribute(value, type);
    }
Returns the attribute value for the given property value. If this
returns undefined, the property will *not* be reflected to an attribute.
If this returns null, the attribute will be removed, otherwise the
attribute will be set to the value.
This uses the property's `reflect` and `type.toAttribute` property options.
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