Segmentation fault 11 DFS maze solution

What seems to be the error? it keeps returning segmentation fault 11. this is supposed to be a solution to a maze using DFS. ............................... ...............................

std::vector<MazeNode> solveDFS(Maze &a_maze){   
MazeNode* nextNode = a_maze.getFirstNode(); 
std::vector<MazeNode> nodes; 
std::stack<MazeNode*> nodesPtr;

nextNode->setVisited();//set origin as visited 
nodesPtr.push(a_maze.getFirstNode());//add origin to stack
nodes.push_back(*a_maze.getFirstNode());//first node added to vector
//cout << a_maze.getFirstNode() << endl;

while(!nodesPtr.empty()){
MazeNode* TopStack = nodesPtr.top();
if(canTravel(TopStack->getDirectionNode(directions::NORTH))){
   nextNode = TopStack->getDirectionNode(directions::NORTH); 
   nextNode->setVisited(); 
   nodesPtr.push(nextNode);
   nodes.push_back(*nextNode);  
}

else if(canTravel(TopStack->getDirectionNode(directions::WEST))){
   nextNode = TopStack->getDirectionNode(directions::WEST); 
   nextNode->setVisited(); 
   nodesPtr.push(nextNode);
   nodes.push_back(*nextNode);
}

else if(canTravel(TopStack->getDirectionNode(directions::SOUTH))){
   nextNode = TopStack->getDirectionNode(directions::SOUTH); 
   nextNode->setVisited(); 
   nodesPtr.push(nextNode);
   nodes.push_back(*nextNode);
}

else if(canTravel(TopStack->getDirectionNode(directions::EAST))){
   nextNode = TopStack->getDirectionNode(directions::EAST); 
   nextNode->setVisited(); 
   nodesPtr.push(nextNode);
   nodes.push_back(*nextNode);
}

else{
    nodesPtr.pop();
}
}
return nodes;
}