coder decodeParams with empty string leads to BigNumber error

[ethers]

using web3.js 0.5.0 via atmospherejs.com

when an eth_call returns 0x, SolidityFunction.unpackOutput slices it into "" which gets passed to decodeParams and an eventual error. Here's the trace:

Exception in template helper: BigNumber Error: new BigNumber() not a base 16 number: 
    at raise (http://localhost:3000/packages/ethereum_web3.js?8c764ae35219eaf9f3601ba16b9a461c7fca0972:6755:25)
    at http://localhost:3000/packages/ethereum_web3.js?8c764ae35219eaf9f3601ba16b9a461c7fca0972:6743:33
    at new BigNumber (http://localhost:3000/packages/ethereum_web3.js?8c764ae35219eaf9f3601ba16b9a461c7fca0972:5790:28)
    at require.1.SolidityType.formatOutput (http://localhost:3000/packages/ethereum_web3.js?8c764ae35219eaf9f3601ba16b9a461c7fca0972:132:22)
    at http://localhost:3000/packages/ethereum_web3.js?8c764ae35219eaf9f3601ba16b9a461c7fca0972:252:29
    at Array.map (native)
    at require.1.SolidityCoder.decodeParams (http://localhost:3000/packages/ethereum_web3.js?8c764ae35219eaf9f3601ba16b9a461c7fca0972:249:18)
    at require.18.SolidityFunction.unpackOutput (http://localhost:3000/packages/ethereum_web3.js?8c764ae35219eaf9f3601ba16b9a461c7fca0972:2810:24)
    at require.18.SolidityFunction.call (http://localhost:3000/packages/ethereum_web3.js?8c764ae35219eaf9f3601ba16b9a461c7fca0972:2831:21)

[frozeman]

@debris i'm not 100% sure about this but the following code could fix it, can you take a look:

SolidityType.prototype.formatOutput = function (param, arrayType) {
    if (arrayType) {
        // let's assume, that we solidity will never return long arrays :P 
        var result = [];
        var paramSlice = param.dynamicPart().slice(0, 64);
        var length = (paramSlice !== '') ? new BigNumber(paramSlice, 16) : 0; // <<---
        for (var i = 0; i < length * 64; i += 64) {
            result.push(this._outputFormatter(new SolidityParam(param.dynamicPart().substr(i + 64, 64))));
        }
        return result;
    }
    return this._outputFormatter(param);
};

[debris]

this error probably occurred, cause empty array was not properly formatted by geth/cpp/python. 0x was returned instead of "0x00000000000000000000000000000000000000000000000000000000000000200000000000000000000000000000000000000000000000000000000000000000".

There is a test for it here. I've checked how empty array is being returned in latest geth (0.9.39) and it's working as expected.