TROUBLESHOOTING: af:query does not search when in query field, String is used

This is an ADF newbie tip.

Problem
Let's say you got a af:query with one query field (of type String) and a result table (typical scenario).
You can search using Number but you cannot search (it brings everything) using String.
No error occurs.

Solution
The bind var of the query field is of type Number, which is the wrong type. Change it to String.