fix inference of object members when a method has no target

pkg/analyzer/lib/src/generated/static_type_analyzer.dart

Index: pkg/analyzer/lib/src/generated/static_type_analyzer.dart
diff --git a/pkg/analyzer/lib/src/generated/static_type_analyzer.dart b/pkg/analyzer/lib/src/generated/static_type_analyzer.dart
index 433bae1c7051d9200cd0790eaad8cb706a1b6d0d..c9efc5d5735cb33a3d146d0a027f570f5745d20d 100644
--- a/pkg/analyzer/lib/src/generated/static_type_analyzer.dart
+++ b/pkg/analyzer/lib/src/generated/static_type_analyzer.dart
@@ -1762,6 +1762,15 @@ class StaticTypeAnalyzer extends SimpleAstVisitor<Object> {
    * being called is one of the object methods.
    */
   bool _inferMethodInvocationObject(MethodInvocation node) {
+    // If we have a call like `toString()` don't infer it.
+    //
+    // Either: it's really `this.toString()` and we shouldn't need inference,
+    // or it's a call to a function that happens to be called `toString()` and
+    // we shouldn't infer.
+    if (node.target == null) {
+      return false;
+    }
+
     // Object methods called on dynamic targets can have their types improved.
     String name = node.methodName.name;
     MethodElement inferredElement =