Sole Suggester: AnalyzingInfixLookupFactory - Store Lookup build failed - solr

Question

I have this configuration (with solr 5.3.1):
<searchComponent class="solr.SuggestComponent" name="suggest">
<lst name="suggester">
<str name="name">suggest</str>
<str name="storeDir">dict_suggest</str>
<str name="lookupImpl">AnalyzingInfixLookupFactory</str>
<str name="highlight">false</str>
<str name="field">suggestion</str>
<str name="suggestAnalyzerFieldType">suggest</str>
<str name="dictionaryImpl">DocumentDictionaryFactory</str>
<str name="payloadField">id</str>
<str name="buildOnStartup">false</str>
<str name="buildOnCommit">false</str>
</lst>
</searchComponent>
<requestHandler name="/suggest" class="solr.SearchHandler" startup="lazy">
<lst name="defaults">
<str name="echoParams">explicit</str>
<str name="suggest">true</str>
<str name="suggest.dictionary">suggest</str>
<str name="suggest.count">10</str>
</lst>
<arr name="components">
<str>suggest</str>
</arr>
</requestHandler>
The field in schema.xml is defined as <field name="suggestion" type="suggest" indexed="true" stored="true" required="true" multiValued="true" />.
The field type definition is this:
<fieldType name="suggest" class="solr.TextField" positionIncrementGap="100">
<analyzer>
<tokenizer class="solr.WhitespaceTokenizerFactory"/>
<filter class="solr.LowerCaseFilterFactory"/>
</analyzer>
</fieldType>
Each time I try to build the index, solr shows Store Lookup build failed
There's no dump or description in the logs.
Am I missing something in the config? The suggester seems to work fine, so the "in memory" index works fine.
Thanks