WitnessUpdateContract constructor
      
      WitnessUpdateContract({ 
    
- required TronAddress ownerAddress,
 - List<
int> ? updateUrl, 
Create a new WitnessUpdateContract instance with specified parameters.
Implementation
WitnessUpdateContract({required this.ownerAddress, List<int>? updateUrl})
    : updateUrl = BytesUtils.tryToBytes(updateUrl, unmodifiable: true);