don't attach info to null cert

lib/core.js

@@ -257,17 +257,26 @@ module.exports.create = function (le) {
           });
         });
       }
+      // Certificates
     , renewAsync: function (args) {
-        // TODO fetch email address if not present
+        // TODO fetch email address (accountBydomain) if not present
         return core.certificates.registerAsync(args);
       }
+      // Certificates
     , checkAsync: function (args) {
         var copy = utils.merge(args, le);
         utils.tplCopy(copy);
 
         // returns pems
-        return le.store.certificates.checkAsync(copy).then(utils.attachCertInfo);
+        return le.store.certificates.checkAsync(copy).then(function (cert) {
+          if (cert) {
+            return utils.attachCertInfo(cert);
+          }
+
+          return null;
+        });
       }
+      // Certificates
     , getAsync: function (args) {
         var copy = utils.merge(args, le);
         args = utils.tplCopy(copy);