Expands on previous function RTT to support named/optional parameters.

compiler/lib/implementation/string_buffer.dart

Index: compiler/lib/implementation/string_buffer.dart
diff --git a/compiler/lib/implementation/string_buffer.dart b/compiler/lib/implementation/string_buffer.dart
index ff39b13a1752da9ad7e8efd88a9bf55ee3d5a1df..373c78d37a1f851e0f7c80816bc7792285d9fad8 100644
--- a/compiler/lib/implementation/string_buffer.dart
+++ b/compiler/lib/implementation/string_buffer.dart
@@ -42,6 +42,9 @@ class StringBufferImpl implements StringBuffer {
    * Adds all items in [objects] to the buffer. Returns [this].
    */
   StringBuffer addAll(Collection<Object> objects) {
+    if (objects == null) {
+      throw const NullPointerException();
+    }
     for (Object obj in objects) {
       add(obj);
     }