Fix a crash in Chain.terse and Chain.foldFrames.

lib/src/chain.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library stack_trace.chain;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:math' as math;
 
@@ skipping 19 matching lines @@
 /// the zone can be handled, along with their associated chains, with the
 /// `onError` callback. For example:
 ///
 ///     Chain.capture(() {
 ///       // ...
 ///     }, onError: (error, stackChain) {
 ///       print("Caught error $error\n"
 ///             "$stackChain");
 ///     });
 class Chain implements StackTrace {
-
   /// The stack traces that make up this chain.
   ///
   /// Like the frames in a stack trace, the traces are ordered from most local
   /// to least local. The first one is the trace where the actual exception was
   /// raised, the second one is where that callback was scheduled, and so on.
   final List<Trace> traces;
 
   /// The [StackZoneSpecification] for the current zone.
   static StackZoneSpecification get _currentSpec =>
     Zone.current[#stack_trace.stack_zone.spec];
@@ skipping 97 matching lines @@
   ///
   /// If [terse] is true, this will also fold together frames from the core
   /// library or from this package, and simplify core library frames as in
   /// [Trace.terse].
   Chain foldFrames(bool predicate(Frame frame), {bool terse: false}) {
     var foldedTraces = traces.map(
         (trace) => trace.foldFrames(predicate, terse: terse));
     var nonEmptyTraces = foldedTraces.where((trace) {
       // Ignore traces that contain only folded frames.
       if (trace.frames.length > 1) return true;
+      if (trace.frames.isEmpty) return false;
 
       // In terse mode, the trace may have removed an outer folded frame,
       // leaving a single non-folded frame. We can detect a folded frame because
       // it has no line information.
       if (!terse) return false;
       return trace.frames.single.line != null;
     });
 
     // If all the traces contain only internal processing, preserve the last
     // (top-most) one so that the chain isn't empty.
@@ skipping 19 matching lines @@
 
     // Don't call out to [Trace.toString] here because that doesn't ensure that
     // padding is consistent across all traces.
     return traces.map((trace) {
       return trace.frames.map((frame) {
         return '${padRight(frame.location, longest)}  ${frame.member}\n';
       }).join();
     }).join(chainGap);
   }
 }