How to deal with information that arrives null? - NoSuchMethodError-CodePudding

I'm getting null information from a web api. If a single information is null, the error will occur:

Error: Exception: NoSuchMethodError: '[]' Dynamic call of null. Receiver: null Arguments: ["address"]

I declared this information in the model like this:

final String? address;

..
address: json['data1']['data2'][0]['data3']['address'][0]

I tried to do something like:

address: json['data1']['data2'][0]['data3']['address'][0].isEmpty ? '' : json['data1']['data2'][0]['data3']['address'][0],

But it does not work.

I appreciate if anyone can help me analyze it!

CodePudding user response：

The only thing you can do is to anticipate the null values and handle each case as needed.

For instance, if a null value is not accepted at all, you could wrap the code in throw ... catch statement then throw an error -- e.g.Missing Data and handle that error.

If having a null value is fine, you can use the null aware operator ? (or a nested if-statements if you prefer that). For example, assuming the value is a String, you could do something like this:

final String? myValue = json['data1']?['data2']?[0]?['data3']?['address']?[0];

Though, keep in mind if you're accessing a list by index, you still can get a RangeError if the index is out of range or if the list is empty. In such case you may need to split the process in a separate method and inspect each part separately such as:

String? extractValue(Map<String, dynamic> json) {
  final firstList = json['data1']?['data2'];
  if (firstList is List && firstList.isNotEmpty) {
    final innerList = firstList[0]['data3']?['address'];
    if (innerList is List && innerList.isNotEmpty) {
      return innerList[0];
    }
  }
  return null; // or return a default value or throw an error
}