Simplify conversion of empty lists to null.

pkg/analysis_server/lib/src/computer/computer_overrides.dart

Index: pkg/analysis_server/lib/src/computer/computer_overrides.dart
diff --git a/pkg/analysis_server/lib/src/computer/computer_overrides.dart b/pkg/analysis_server/lib/src/computer/computer_overrides.dart
index 8140be5b1248358b00a5d6f0d4abee5b34aaeeb0..ca6c9595eebcc2826013382caf4cce82805d2242 100644
--- a/pkg/analysis_server/lib/src/computer/computer_overrides.dart
+++ b/pkg/analysis_server/lib/src/computer/computer_overrides.dart
@@ -4,6 +4,7 @@
 
 library computer.overrides;
 
+import 'package:analysis_server/src/collections.dart';
 import 'package:analysis_server/src/protocol.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart' as engine;
@@ -75,7 +76,7 @@ class DartUnitOverridesComputer {
               offset,
               length,
               superclassMember: superMember,
-              interfaceMembers: interfaceMembers.isEmpty ? null : interfaceMembers));
+              interfaceMembers: nullIfEmpty(interfaceMembers)));
     }
   }