What does "Missing sort order" error mean

[Phillip Farber]

Hi,
Just getting my head around Solr queries.  I get HTTP ERROR: 400
Missing sort order. when I issue this query:

http://localhost:8983/solr/select/?q=car&sort=title

My title field is:

  <field name="title" type="myAlphaOnlySort" indexed="true" 
stored="false" required="true"/>

where "myAlphaOnlySort" is based on the alphaOnlySort from the example 
solr.xml:

    <fieldType name="myAlphaOnlySort" class="solr.TextField" 
sortMissingLast="true" omitNorms="true">
      <analyzer>
        <tokenizer class="solr.KeywordTokenizerFactory"/>
        <filter class="solr.LowerCaseFilterFactory" />
        <filter class="solr.TrimFilterFactory" />
      </analyzer>
    </fieldType>

What am I missing?

Regards,
Phil