Not-found addresses cause The method '[]' was called on null.

[willbryant]

If you make a distance matrix call that returns any NOT_FOUND cells, which happens if you give an address that is both incomplete and invalid (eg. "1 Nonexistant Street" with no city), distance.dart throws The method '[]' was called on null. because it tries to dereference JSON keys that don't exist.

Here's the stacktrace:

#0      Object.noSuchMethod (dart:core-patch/object_patch.dart:54:5)
#1      _$ValueFromJson (package:google_maps_webservice/src/distance.g.dart:66:16)
#2      new Value.fromJson (package:google_maps_webservice/src/distance.dart:328:56)
#3      _$ElementFromJson (package:google_maps_webservice/src/distance.g.dart:52:21)
#4      new Element.fromJson (package:google_maps_webservice/src/distance.dart:317:7)
#5      _$RowFromJson.<anonymous closure> (package:google_maps_webservice/src/distance.g.dart:40:34)
#6      MappedListIterable.elementAt (dart:_internal/iterable.dart:412:31)
#7      ListIterator.moveNext (dart:_internal/iterable.dart:341:26)
#8      new _GrowableList._ofEfficientLengthIterable (dart:core-patch/growable_array.dart:188:27)
#9      new _GrowableList.of (dart:core-patch/growable_array.dart:150:28)
#10     new List.of (dart:core-patch/array_patch.dart:50:28)
#11     ListIterable.toList (dart:_internal/iterable.dart:212:44)
#12     _$RowFromJson (package:google_maps_webservice/src/distance.g.dart:41:14)
#13     new Row.fromJson (package:google_maps_webservice/src/distance.dart:300:54)
#14     _$DistanceResponseFromJson.<anonymous closure> (package:google_maps_webservice/src/distance.g.dart:22:30)
#15     MappedListIterable.elementAt (dart:_internal/iterable.dart:412:31)
#16     ListIterator.moveNext (dart:_internal/iterable.dart:341:26)
#17     new _GrowableList._ofEfficientLengthIterable (dart:core-patch/growable_array.dart:188:27)
#18     new _GrowableList.of (dart:core-patch/growable_array.dart:150:28)
#19     new List.of (dart:core-patch/array_patch.dart:50:28)
#20     ListIterable.toList (dart:_internal/iterable.dart:212:44)
#21     _$DistanceResponseFromJson (package:google_maps_webservice/src/distance.g.dart:23:14)
#22     new DistanceResponse.fromJson (package:google_maps_webservice/src/distance.dart:289:7)
#23     GoogleDistanceMatrix._decode (package:google_maps_webservice/src/distance.dart:254:24)
#24     GoogleDistanceMatrix._distance (package:google_maps_webservice/src/distance.dart:60:12)
<asynchronous suspension>
#25     StackZoneSpecification._registerUnaryCallback.<anonymous closure> (package:stack_trace/src/stack_zone_specification.dart)
<asynchronous suspension>

And here's an example maps API response showing the NOT_FOUND elements:

{
   "destination_addresses" : [ "1 Tasman Street, Mount Cook, Wellington 6021, New Zealand", "" ],
   "origin_addresses" : [
      "Elizabeth Street at Kent Terrace, Wellington 6011, New Zealand",
      "1 Tasman Street, Mount Cook, Wellington 6021, New Zealand",
      ""
   ],
   "rows" : [
      {
         "elements" : [
            {
               "distance" : {
                  "text" : "1.2 km",
                  "value" : 1159
               },
               "duration" : {
                  "text" : "3 mins",
                  "value" : 205
               },
               "status" : "OK"
            },
            {
               "status" : "NOT_FOUND"
            }
         ]
      },
      {
         "elements" : [
            {
               "distance" : {
                  "text" : "1 m",
                  "value" : 0
               },
               "duration" : {
                  "text" : "1 min",
                  "value" : 0
               },
               "status" : "OK"
            },
            {
               "status" : "NOT_FOUND"
            }
         ]
      },
      {
         "elements" : [
            {
               "status" : "NOT_FOUND"
            },
            {
               "status" : "NOT_FOUND"
            }
         ]
      }
   ],
   "status" : "OK"
}

[willbryant]

I think the issue is here:

class Element {
  final Value distance;
  final Value duration;
  final String? elementStatus;

distance and duration both need to have type Value? as they are not present in the NOT_FOUND case.