don't pin falsey document ids

lib/commands/pin-rpc.js

@@ -162,7 +162,7 @@ Pinning.pinChannel = function (Env, safeKey, channels, cb) {
 
         // only pin channels which are not already pinned
         var toStore = channels.filter(function (channel) {
-            return pinned.indexOf(channel) === -1;
+            return channel && pinned.indexOf(channel) === -1;
         });
 
         if (toStore.length === 0) {
@@ -204,7 +204,7 @@ Pinning.unpinChannel = function (Env, safeKey, channels, cb) {
 
         // only unpin channels which are pinned
         var toStore = channels.filter(function (channel) {
-            return pinned.indexOf(channel) !== -1;
+            return channel && pinned.indexOf(channel) !== -1;
         });
 
         if (toStore.length === 0) {