How to get rows where count() is null?
OK, without any detailed info about the tables' relationships (1-1, 1-to-many, many-to-many) and the primary keys, it's not easy to deal with this. But lets try.

The FROM clause has a 6-table join:

FROM 
  Bac              b0_  INNER JOIN 
  Bachelier        b4_   ON b0_.bachelier_cne = b4_.cne INNER JOIN 
  EtablissementBac e5_   ON b0_.etabBac_id = e5_.codeLieu INNER JOIN 
  Delegation       d1_   ON e5_.delegation_id = d1_.codeLieu INNER JOIN 
  MentionBac       m2_   ON b0_.mentionBac_id = m2_.codeMention INNER JOIN 
  TypeBac          t3_   ON b0_.typeBac_id = t3_.codeType


Since 2 tables (m2_ and t3_) are involved in the WHERE clause:

WHERE m2_.codeMention IN ('TB',  'B')
  AND t3_.codeType IN ('114',  '129')


and one more (d1_) in the GROUP BY clause:

GROUP BY 
  d1_.codeLieu, 
  m2_.codeMention, m2_.libelleMention, 
  t3_.codeType, t3_.libelleType, t3_.abbrType


we'll assume that these 3 should be join with proper INNER joins.

And since you are counting on b0_, this will probably have to be "LEFT" joined. That leaves with some choices about the other two tables (b4_ and e5_). So, lets rewrite the FROM part. First the 3 (sure JOIN) tables, then the ambiguous 2 and lastly the sure (LEFT JOIN) b0_:

FROM 
  TypeBac          t3_  INNER JOIN 
  MentionBac       m2_  INNER JOIN 
  Delegation       d1_  INNER JOIN 

  EtablissementBac e5_   ON e5_.delegation_id = d1_.codeLieu INNER JOIN 
  Bachelier        b4_  
                        LEFT JOIN
  Bac              b0_   ON b0_.bachelier_cne = b4_.cne 
                        AND b0_.etabBac_id = e5_.codeLieu 
                        AND b0_.typeBac_id = t3_.codeType
                        AND b0_.mentionBac_id = m2_.codeMention 


Well, that doesn't look correct. Because (except for the d1 - e5 join), we don't have a way to join the other 4 tables. All 4 are to be joined with the b4 which has to be last (as we want to LEFT JOIN it.) This observation leaves with one choice:

FROM 
  TypeBac          t3_  CROSS JOIN 
  MentionBac       m2_  CROSS JOIN 
  Delegation       d1_  INNER JOIN 

  EtablissementBac e5_   ON e5_.delegation_id = d1_.codeLieu 
                        CROSS JOIN 
  Bachelier        b4_  
                        LEFT JOIN
  Bac              b0_   ON b0_.bachelier_cne = b4_.cne 
                        AND b0_.etabBac_id = e5_.codeLieu 
                        AND b0_.typeBac_id = t3_.codeType
                        AND b0_.mentionBac_id = m2_.codeMention 


Try changing the FROM clause as above. The only other option I see is the removal of the CROSS JOIN  Bachelier  b4_, as no column of this table is included in the SELECT.



After more comments and a request, here is one final trial:

SELECT COUNT( b0_.id ) AS sclr0, 
       d1_.codeLieu AS codeLieu1, d1_.nomLieu AS nomLieu2, 
         d1_.lngLieu AS lngLieu3, d1_.latLieu AS latLieu4, 
       m2_.libelleMention AS libelleMention5, 
       t3_.libelleType AS libelleType6
FROM 
  TypeBac          t3_  
    CROSS JOIN 
  MentionBac       m2_  
    CROSS JOIN 
  Delegation       d1_  
    INNER JOIN 
  EtablissementBac e5_   ON e5_.delegation_id = d1_.codeLieu 
    LEFT JOIN
  Bac              b0_   ON b0_.etabBac_id = e5_.codeLieu 
                        AND b0_.typeBac_id = t3_.codeType
                        AND b0_.mentionBac_id = m2_.codeMention 
WHERE m2_.codeMention IN ('TB',  'B')
  AND t3_.codeType IN ('114',  '129')
  AND EXISTS
        ( SELECT *
          FROM Bac b
          WHERE b.etabBac_id = e5_.codeLieu 
            AND b.typeBac_id = t3_.codeType
            AND b.mentionBac_id = m2_.codeMention 
        )
GROUP BY 
    d1_.codeLieu, 
    m2_.codeMention, m2_.libelleMention, 
    t3_.codeType, t3_.libelleType, t3_.abbrType ;