code: function (vmTraceIndex, trace) {
      var step = trace[vmTraceIndex]
      if (this.isCreateInstruction(step)) {
        return this.contractCreationToken(vmTraceIndex)
      } else if (this.isCallInstruction(step)) {
        var stack = step.stack // callcode, delegatecall, ...
        return ui.normalizeHexAddress(stack[stack.length - 2])
      }
      return undefined
    }
docs: vmTraceIndex has to point to a CALL, CODECALL, ...