fix crash when encoding Error object

example/pubspec.lock

@@ -75,7 +75,7 @@ packages:
       path: ".."
       relative: true
     source: path
-    version: "0.3.6"
+    version: "0.3.7"
   flutter_test:
     dependency: "direct dev"
     description: flutter
@@ -95,6 +95,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "0.12.11"
+  material_color_utilities:
+    dependency: transitive
+    description:
+      name: material_color_utilities
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "0.1.4"
   meta:
     dependency: transitive
     description:
@@ -108,7 +115,7 @@ packages:
       name: path
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.8.0"
+    version: "1.8.1"
   sky_engine:
     dependency: transitive
     description: flutter
@@ -120,7 +127,7 @@ packages:
       name: source_span
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.8.1"
+    version: "1.8.2"
   stack_trace:
     dependency: transitive
     description:
@@ -155,7 +162,7 @@ packages:
       name: test_api
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.4.3"
+    version: "0.4.9"
   typed_data:
     dependency: transitive
     description:
@@ -169,7 +176,7 @@ packages:
       name: vector_math
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.1"
+    version: "2.1.2"
 sdks:
   dart: ">=2.14.0 <3.0.0"
   flutter: ">=1.20.0"