Update field in Lucene / Examine index (Umbraco 8 v8 -specific)

update examine fields.cs

var index = (LuceneIndex)ExamineManager.Instance.Indexes.Where(f => f.Name == "ExternalIndex").FirstOrDefault();

// Get the IndexWriter
var writer = index.GetIndexWriter();

var searcher = (BaseLuceneSearcher)index.GetSearcher();

// perform search to get the doc from the index based on node id
Term term = new Term("id", "1082"); // Term to get node by id
var q = new TermQuery(term);

var sres = searcher.GetLuceneSearcher().Search(q, 1);

var doc = searcher.GetLuceneSearcher().Doc(sres.ScoreDocs.First().Doc);
doc.RemoveFields("testing");
doc.Add(new Field("testing", "Hallo world mamma", Field.Store.YES, Field.Index.ANALYZED));

writer.UpdateDocument(term,doc);
//writer.Commit();
//writer.Optimize();