Auction project in Solidity: Why do I get "VM error: invalid opcode" for this code?

Question

I am trying to do an Auction project and this part is bugging me. I can't figure out what is the problem that's causing the following error message: "VM error: invalid opcode.". Even if I do this simple smart contact I get the same error message. So I would like it if someone can figure out what is the problem with the provided smart contract. Thanks!

// SPDX-License-Identifier: UNLICENSED
pragma solidity >=0.6.0 < 0.7.0;

contract testing {
    
    mapping(address => uint256[]) fundsByBidder;
    mapping(uint256 => uint256) newBidToGoods;
     
    function update(uint256 _goodsId) public payable {
        newBidToGoods[_goodsId] = fundsByBidder[msg.sender][_goodsId] + msg.value;
    }
    
    function show(uint256 _goodsId) public view returns(uint256) {
        return newBidToGoods[_goodsId];
    }
}

Answer 1

Because fundsByBidder[msg.sender].length is not larger than _goodsId.