Take a look in web-framework-config-application.xml:
<config evaluator="string-compare" condition="Search" replace="true">
<search>
<!– default minimum length for search terms –>
<min-search-term-length>1</min-search-term-length>
<!– default maximum number of results for a search –>
<max-search-results>100</max-search-results>
</search>
</config>
Change min-search-term-length to 0.