anchor.diff:      ast.CallExpression expression,
       hir.IdentifierExpression target,
     ) {
  +    assert(target != null);
       assert(target.identifier is hir.PropertyIdentifier);
       final identifier = target.identifier as hir.PropertyIdentifier;
   
  
positive.code: import 'package:dartx/dartx.dart';
  import 'package:parser/parser.dart' as ast;
  import 'package:parser/parser.dart' show SourceSpan;
  
negative.code:       final value = entry.value.expression;
  
        final innerContext = innerExpressionContext(
          expressionType: Option.some(
            parametersByName[name].type.bakeGenerics(genericsMap),
          ),
        );
        final lowered = innerContext.lowerUnambiguous(value);
        if (lowered is Error) {
  