stacktrace dart

Crash when compiling null,
at character offset null:
org-dartlang-app:///packages/braver_patient/models.dart: Internal problem: Unhandled Null in finalizeExports.
#0      internalProblem (package:front_end/src/fasta/problems.dart:52:5)
#1      unhandled (package:front_end/src/fasta/problems.dart:71:10)
#2      DillLibraryBuilder.finalizeExports (package:front_end/src/fasta/dill/dill_library_builder.dart:394:11)
#3      DillLibraryBuilder.ensureLoaded (package:front_end/src/fasta/dill/dill_library_builder.dart:127:7)
#4      LazyLibraryScope.ensureScope (package:front_end/src/fasta/dill/dill_library_builder.dart:61:21)
#5      LazyScope._local (package:front_end/src/fasta/scope.dart:645:5)
#6      Scope.forEach (package:front_end/src/fasta/scope.dart:535:5)
#7      Import.finalizeImports (package:front_end/src/fasta/import.dart:77:27)
#8      SourceLibraryBuilder.addImportsToScope (package:front_end/src/fasta/source/source_library_builder.dart:1368:14)
#9      SourceLoader.computeLibraryScopes (package:front_end/src/fasta/source/source_loader.dart:1373:23)
#10     KernelTarget.buildOutlines.<anonymous closure> (package:front_end/src/fasta/kernel/kernel_target.dart:434:14)
#11     withCrashReporting (package:front_end/src/fasta/crash.dart:122:24)
#12     KernelTarget.buildOutlines (package:front_end/src/fasta/kernel/kernel_target.dart:417:12)
#13     IncrementalCompiler.computeDelta.<anonymous closure> (package:front_end/src/fasta/incremental_compiler.dart:407:59)
<asynchronous suspension>
#14     computeKernel (package:frontend_server/compute_kernel.dart:370:9)
<asynchronous suspension>
#15     KernelWorker.performRequest (file:///opt/s/w/ir/x/w/sdk/utils/bazel/kernel_worker.dart:70:20)
<asynchronous suspension>
#16     AsyncWorkerLoop.run (package:bazel_worker/src/worker/async_worker_loop.dart:35:20)
<asynchronous suspension>
#17     main (file:///opt/s/w/ir/x/w/sdk/utils/bazel/kernel_worker.dart:32:5)
<asynchronous suspension>