Accordingly to section JSP.2.3.7 of the spec.
The empty operator is a prefix operator that can be used to determine if a value is null or empty.
To evaluate empty A
� If A is null, return true,
� Otherwise, if A is the empty string, then return true.
� Otherwise, if A is an empty array, then return true.
� Otherwise, if A is an empty Map, return true,
� Otherwise, if A is an empty Collection, return true,
� Otherwise return false.