why Solr suggest return empty result?

i am trying to build a simple suggester using Solr 6.6, i have followed the tutorial in Apache,and here is my solrconfig.xml added components:

 <searchComponent name="suggest" class="solr.SuggestComponent">
 <lst name="suggester">
 <str name="name">mySuggester</str>
 <str name="lookupImpl">FuzzyLookupFactory</str>
 <str name="dictionaryImpl">DocumentDictionaryFactory</str>
 <str name="field">name_auto</str>
 <str name="suggestAnalyzerFieldType">suggestName</str>
 <str name="buildOnStartup">false</str>

  <requestHandler name="/suggest" class="solr.SearchHandler" startup="lazy">
<lst name="defaults">
  <str name="suggest">true</str>
  <str name="suggest.count">10</str>
              <str name="suggest.dictionary">mySuggester</str>
</lst>
<arr name="components">
  <str>suggest</str>
</arr>

managed-schema fields:

  <fieldType class="solr.TextField" name="suggestName" positionIncrementGap="100">
<analyzer>
  <tokenizer class="solr.StandardTokenizerFactory"/>
  <filter class="solr.StandardFilterFactory"/>
  <filter class="solr.LowerCaseFilterFactory"/>
</analyzer>

<field name="name_auto" type="string" indexed="true" stored="true"/>
<copyField source="name" dest="name_auto"/>

after done of configuration i have build the using Solr API:

/suggest?suggest=true&suggest.build=true&suggest.dictionary=mySuggester&wt=json&suggest.q=shroof

the final result were empty array of suggestions