dartdoc failed: type 'UndefinedElementType' is not a subtype of type 'DefinedElementType'

[sigurdm]

Seen on pub.

Happens for the package:
https://storage.googleapis.com/pub-packages/packages/dart_extension_methods-0.1.0.tar.gz

Command:

$ dartdoc .

Version:

$ dartdoc --version
dartdoc version: 0.29.1

Full stacktrace:

dartdoc failed: type 'UndefinedElementType' is not a subtype of type 'DefinedElementType'
package:dartdoc/src/model.dart 1342:5                                       new Extension
package:dartdoc/src/model.dart 3289:29                                      new ModelElement.from
package:dartdoc/src/model.dart 2525:36                                      Library.extensions.<fn>
dart:core                                                                   Iterable.toList
package:dartdoc/src/model.dart 2526:12                                      Library.extensions
package:dartdoc/src/model.dart 2941:17                                      Library.modelElementsMap
package:dartdoc/src/model.dart 2982:47                                      Library.allModelElements
package:dartdoc/src/model.dart 5868:48                                      PackageGraph.allModelElements.<fn>.<fn>
dart:collection                                                             SetMixin.forEach
package:dartdoc/src/model.dart 5867:18                                      PackageGraph.allModelElements.<fn>
dart:collection                                                             SetMixin.forEach
package:dartdoc/src/model.dart 5861:52                                      PackageGraph.allModelElements
package:dartdoc/src/model.dart 5121:28                                      PackageGraph.precacheLocalDocs
dart:core                                                                   Iterable.toList
package:dartdoc/src/model.dart 5074:56                                      PackageGraph.initializePackageGraph
package:dartdoc/src/model.dart 6908:20                                      PackageBuilder.buildPackageGraph
===== asynchronous gap ===========================
package:dartdoc/dartdoc.dart 95:26                                          Dartdoc.generateDocsBase
package:dartdoc/dartdoc.dart 134:43                                         Dartdoc.generateDocs
dart:async                                                                  runZoned
/b/s/w/ir/cache/builder/sdk/third_party/pkg/dartdoc/bin/dartdoc.dart 96:13  main.<fn>
package:stack_trace                                                         Chain.capture
/b/s/w/ir/cache/builder/sdk/third_party/pkg/dartdoc/bin/dartdoc.dart 95:17  main

[jcollins-g]

reproduced at head + #2109.

[jcollins-g]

dartdoc does not consider that extensions on dynamic might exist.

/// 
extension LogExtensions on dynamic {}

This is therefore fatal.