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pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart

Index: pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
index b675255092ade45252f24370ef4bcb4bb7c91c0b..6ab5beed259b2b12a06bdad020c23797eaa40836 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
@@ -24,6 +24,7 @@ import '../util/relativize.dart' show relativizeUri;
 import 'kernel_builder.dart'
     show
         Builder,
+        BuiltinTypeBuilder,
         ClassBuilder,
         ConstructorReferenceBuilder,
         DynamicTypeBuilder,
@@ -314,6 +315,8 @@ class KernelLibraryBuilder
       library.addClass(builder.build(this));
     } else if (builder is PrefixBuilder) {
       // Ignored. Kernel doesn't represent prefixes.
+    } else if (builder is BuiltinTypeBuilder) {
+      // Nothing needed.
     } else {
       internalError("Unhandled builder: ${builder.runtimeType}");
     }