| 1234567891011121314151617 | var filter = require('./filter');    function isValidString(val) {        return (val != null && val !== '');    }    /**     * Joins strings with the specified separator inserted between each value.     * Null values and empty strings will be excluded.     */    function join(items, separator) {        separator = separator || '';        return filter(items, isValidString).join(separator);    }    module.exports = join;
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