anchor.diff:              ? documentation
               : this.documentation,
           description: description != null ? description : this.description,
  +        environment: environment != null ? environment : this.environment,
           dependencies: dependencies != null ? dependencies : this.dependencies,
           devDependencies: devDependencies != null
               ? devDependencies
  
positive.code:       ..add('version', version)
        ..add('homepage', homepage)
        ..add('documentation', documentation)
        ..add('description', description)
        ..add('dependencies', dependencies)
        ..add('dev_dependencies', devDependencies)
  
negative.code:               .readAsString()));
  
    PubSpec copy({String name, String author, Version version, String homepage,
        String documentation, String description, Environment environment,
        Map<String, DependencyReference> dependencies,
        Map<String, DependencyReference> devDependencies,
        Map<String, DependencyReference> dependencyOverrides, Map unParsedYaml}) {
  