Hi, I have a problem with this query, it tells me the error

ORA-00932: inconsistent datatypes: expected NCHAR got NUMBER
00932. 00000 -  "inconsistent datatypes: expected %s got %s"
*Cause:    
*Action:
Error en la línea: 54, columna: 43

I think the problem is because I should cast 10 or something like that, try this post Post 1 adding n '' ahead of 10 but it did not work because the code turns blue. I also tried this Post 2 that says you have to add an N '' || before 10 and the same thing happens ...

SELECT NOMBRE, COALESCE(DIRECCION,CORREO, 10) comm
FROM ESTUDIANTE
WHERE GENERO_A =   
   (SELECT GENERO_A
    FROM ESTUDIANTE
    GROUP BY GENERO_A
    HAVING COUNT(GENERO_A) = 
        (SELECT MAX(COUNT(*)) as CONTAR
        FROM ESTUDIANTE
        GROUP BY GENERO_A))
ORDER BY NOMBRE;