anchor.diff:                    file.createSource(), content, analysisDriver.sourceFactory);
             formatter.formatErrors([new AnalysisErrorInfoImpl(errors, lineInfo)]);
             for (AnalysisError error in errors) {
  -            allResult = allResult.max(determineProcessedSeverity(
  -                error, options, analysisDriver.analysisOptions));
  +            ErrorSeverity severity = determineProcessedSeverity(
  +                error, options, analysisDriver.analysisOptions);
  +            if (severity != null) {
  +              allResult = allResult.max(severity);
  +            }
             }
           } else if (shortName == AnalysisEngine.PUBSPEC_YAML_FILE) {
             try {
  
positive.code:               formatter
                    .formatErrors([new AnalysisErrorInfoImpl(errors, lineInfo)]);
                for (AnalysisError error in errors) {
                  allResult = allResult.max(determineProcessedSeverity(
                      error, options, analysisDriver.analysisOptions));
                }
              }
            } catch (exception) {
  
negative.code:             'Unable to read package config data from $packageConfigPath: $e');
        }
      } else if (options.packageRootPath != null) {
        packageMap = _PackageRootPackageMapBuilder.buildPackageMap(
            options.packageRootPath);
      } else {
        file_system.Resource cwd = resourceProvider.getResource('.');
        // Look for .packages.
  