Resetting index when capping connection pool

lib/connection/pool.js

@@ -217,6 +217,12 @@ Pool.prototype.capConnections = function(maxConnections) {
     var connections = this.connections.slice(maxConnections);
     // Cap the active connections
     this.connections = this.connections.slice(0, maxConnections);
+
+    if (this.index >= maxConnections){
+      // Go back to the beggining of the pool if capping connections
+      this.index = 0;
+    }
+
     // Remove all listeners
     for(var i = 0; i < connections.length; i++) {
       connections[i].removeAllListeners('close');

lib/topologies/server.js

@@ -699,7 +699,8 @@ var executeSingleOperation = function(self, ns, cmd, queryOptions, options, onAl
   var connection = options.connection || self.s.pool.get();
 
   // Double check if we have a valid connection
-  if(!connection.isConnected()) {
+  // Checking that the connection exists to avoid an uncaught exception in case there is an issue with the pool
+  if(!(connection && connection.isConnected())) {
     return callback(new MongoError(f("no connection available to server %s", self.name)));
   }