anchor.diff:    }
   }
   
  -HashSet<Expression> _extractComparisons(BinaryExpression node) {
  -  final HashSet<Expression> comparisons = new HashSet<Expression>.identity();
  +Set<Expression> _extractComparisons(BinaryExpression node) {
  +  final Set<Expression> comparisons = new HashSet<Expression>.identity();
     if (_isComparison(node)) {
       comparisons.add(node);
     }
  
positive.code: import 'package:analyzer/dart/ast/token.dart';
  import 'package:linter/src/util/boolean_expression_utilities.dart';
  
  void _addNodeComparisons(Expression node, HashSet<Expression> comparisons) {
    if (_isComparison(node)) {
      comparisons.add(node);
    } else if (_isBooleanOperation(node)) {
  
negative.code:             : TokenType.AMPERSAND_AMPERSAND);
  
      if (_contradictions.isEmpty) {
        Set<Expression> set = (binaryExpression != null
            ? _extractComparisons(testingExpression)
            : [testingExpression].toSet())
          ..addAll(truths)
  