title: Elasticsearch nest can't find filter
body: <p>So I'm trying to configure my index to have certain mappings and filters, but whenever I try to create the index I get the following error:</p>
  
  <pre><code>"[amgindex] failed to create index]; nested: IllegalArgumentException[Custom Analyzer [amgsearch] failed to find filter under name [synonym]"
  </code></pre>
  
  <p>this is the code I'm using to create the index</p>
  
  <pre><code>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 =&gt; i
                      .Analysis(descriptor =&gt; descriptor
                          .Analyzers(bases =&gt; bases
                              //.Add("amgBasic", amgBasic)
                              //.Add("amgBasicText", amgBasicText)
                              .Add("amgsearch", amgSearch)
                           )
                      .TokenFilters(c =&gt; c.Add("stemmereng", new StemmerTokenFilter() { Language = "english" }))
                      .TokenFilters(c =&gt; c.Add("stemmernl", new StemmerTokenFilter() { Language = "english" }))
                      .TokenFilters(c =&gt; c.Add("stopper", new StopTokenFilter() { Stopwords = new List&lt;string&gt;() { "_english_", "_dutch_" } }))
                      .TokenFilters(c =&gt; c.Add("snowball", new SnowballTokenFilter() { Language = "english" }))
                      .TokenFilters(c =&gt; c.Add("worddelimiter ", new WordDelimiterTokenFilter() { }))
                      .TokenFilters(c =&gt; c.Add("synonym ", synonmyfilter))
  
                      )
                      .AddMapping&lt;general_document&gt;(m =&gt; m
                          .Properties(o =&gt; o
                              .String(p =&gt; p.Name(x =&gt; x.object_name).IndexAnalyzer("amgSearch"))
                              .String(p =&gt; p.Name(x =&gt; x.title).IndexAnalyzer("amgSearch"))
                              .String(p =&gt; p.Name(x =&gt; x.Text).IndexAnalyzer("amgSearch"))
                          )
                      )
                  );
      Log.Info("Index created? " + result.Acknowledged);
    } catch (Exception ex) {
      Log.Error("[index-creation] " + ex.Message);
      throw;
    }
  }
  </code></pre>
  
  <p>everytime I use one of my own filters the error pops up.
  Any clue why this is happening?</p>