crash fixes

src/location.js

@@ -1,7 +1,13 @@
 'use strict';
 
+const assert = require('assert');
+
 class Location {
     constructor(subdomain, domain, type, certificate) {
+        assert(subdomain === null || typeof subdomain === 'string');
+        assert(domain === null || typeof domain === 'string');
+        assert.strictEqual(typeof type, 'string');
+
         this.subdomain = subdomain;
         this.domain = domain;
         this.type = type;