On global search, enter a text and click on enter key. 

On filter, select a thematic, or a project in the list : 

=> 

=> Following error is encountered (for thematic) : 
Caused by: javax.jcr.query.InvalidQueryException: Lexical error at line 1, column 40. Encountered: "]" (93), after : "" for statement: for $v in //element(, ametys:project)[]//element(, ametys:task)[jcr:like(fn:lower-case(@ametys:label), '%ferfezzer%') or jcr:contains(ametys:description, 'ferfezzer')] return $v
at org.apache.jackrabbit.spi.commons.query.xpath.XPathQueryBuilder.<init>(XPathQueryBuilder.java:307)
at org.apache.jackrabbit.spi.commons.query.xpath.XPathQueryBuilder.createQuery(XPathQueryBuilder.java:336)