Null check remover understands JS fragments.

pkg/compiler/lib/src/js/js.dart

 // Copyright (c) 2015, 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 js;
 
 import 'package:js_ast/js_ast.dart';
 export 'package:js_ast/js_ast.dart';
 
 import '../common.dart';
@@ skipping 144 matching lines @@
           }
         }
       }
       _cachedLiteral = js.escapedString(text);
     }
     return _cachedLiteral;
   }
 
   @override
   String get value => _literal.value;
-}
+}
+
+/// Returns `true` if [template] will immediately give a TypeError if the first
+/// placeholder is `null` or `undefined`.
+bool isNullGuardOnFirstArgument(Template template) {
+  // We look for a template of the form
+  //
+  //     #.something
+  //     #.something()
+  //
+  Node node = template.ast;
+  if (node is Call) {
+    Call call = node;
+    node = call.target;
+  }
+  if (node is PropertyAccess) {
+    PropertyAccess access = node;
+    if (access.receiver is InterpolatedExpression) {
+      InterpolatedExpression hole = access.receiver;
+      return hole.isPositional && hole.nameOrPosition == 0;
+    }
+  }
+  return false;
+}