diff --git a/src/voucherify.js b/src/voucherify.js
index 72eb714..6516e1f 100644
--- a/src/voucherify.js
+++ b/src/voucherify.js
@@ -10,7 +10,7 @@ const assertOption = (options, name) => {
 
 const encode = (value = '') => encodeURIComponent(value)
 const isString = (value) => typeof (value) === 'string'
-const isObject = (value) => typeof (value) === 'object' && !Array.isArray(value)
+const isObject = (value) => typeof (value) === 'object' && !Array.isArray(value) && value !== null
 const isFunction = (value) => typeof (value) === 'function'
 
 module.exports = function (options) {