Elasticsearch nest不能找到过滤器

所以我试图配置我的索引有一定的映射和过滤器，但每当我尝试创建索引我得到以下错误:

"[amgindex] failed to create index]; nested: IllegalArgumentException[Custom Analyzer [amgsearch] failed to find filter under name [synonym]"

这是我用来创建索引

public void newIndex() {
  var amgBasic = new CustomAnalyzer {
    Tokenizer = "edgeNGram",
    Filter = new string[] { "lowercase", "worddelimiter", "stemmerEng", "stemmerNl", "stopper", "snowball" } // 
  };
  var amgBasicText = new CustomAnalyzer {
    Tokenizer = "standard",
    Filter = new string[] { "lowercase", "worddelimiter" }
  };
  var amgSearch = new CustomAnalyzer {
    Tokenizer = "whitespace",
    Filter = new string[] { "lowercase", "synonym" }
  };
  var synonmyfilter = new SynonymTokenFilter() {
    Format = "Solr",
    SynonymsPath = "analysis/synonym.txt"
  };

  try {
    var result = client.CreateIndex("amgindex", i => i
                    .Analysis(descriptor => descriptor
                        .Analyzers(bases => bases
                            //.Add("amgBasic", amgBasic)
                            //.Add("amgBasicText", amgBasicText)
                            .Add("amgsearch", amgSearch)
                         )
                    .TokenFilters(c => c.Add("stemmereng", new StemmerTokenFilter() { Language = "english" }))
                    .TokenFilters(c => c.Add("stemmernl", new StemmerTokenFilter() { Language = "english" }))
                    .TokenFilters(c => c.Add("stopper", new StopTokenFilter() { Stopwords = new List<string>() { "_english_", "_dutch_" } }))
                    .TokenFilters(c => c.Add("snowball", new SnowballTokenFilter() { Language = "english" }))
                    .TokenFilters(c => c.Add("worddelimiter ", new WordDelimiterTokenFilter() { }))
                    .TokenFilters(c => c.Add("synonym ", synonmyfilter))
                    )
                    .AddMapping<general_document>(m => m
                        .Properties(o => o
                            .String(p => p.Name(x => x.object_name).IndexAnalyzer("amgSearch"))
                            .String(p => p.Name(x => x.title).IndexAnalyzer("amgSearch"))
                            .String(p => p.Name(x => x.Text).IndexAnalyzer("amgSearch"))
                        )
                    )
                );
    Log.Info("Index created? " + result.Acknowledged);
  } catch (Exception ex) {
    Log.Error("[index-creation] " + ex.Message);
    throw;
  }
}

每次我使用我自己的过滤器时，错误弹出。知道为什么会这样吗?