"IS NOT" syntax error in Java / SQLite application

I'm working on an Java application with SQLite database. I have to execute this query :

select * from service 
where (tache IS NOT 'I') 
AND (idequiv IS null OR idequiv = '' OR idequiv<=0) 
union 
select * from service where (idequiv IS NOT null) 
and (tache IS NOT 'I') 
group by num_service 
order by num_service;

This works well in SQLiteStudio, but in my application I got this exception :

 java.sql.SQLException: near "'I'": syntax error    at
 org.sqlite.DB.throwex(DB.java:288)     at
 org.sqlite.NativeDB.prepare(Native Method)     at
 org.sqlite.DB.prepare(DB.java:114)     at
 org.sqlite.PrepStmt.<init>(PrepStmt.java:37)   at
 o开发者_C百科rg.sqlite.Conn.prepareStatement(Conn.java:231)    at
 org.sqlite.Conn.prepareStatement(Conn.java:224)    at
 org.sqlite.Conn.prepareStatement(Conn.java:213)

Any Idea why ? I'm desperate ..

IS NOT and IS is used for NULL values. Use <> or NOT a = b for values.

SELECT * FROM service 
WHERE (NOT tache = 'I') 
AND (idequiv IS null OR idequiv = '' OR idequiv<=0) 
UNION
SELECT * FROM service 
WHERE (idequiv IS NOT null) 
AND (NOT tache = 'I') 
GROUP BY num_service 
ORDER BY num_service;