I have a package with an overloaded function, wich accepts one parameter (INTEGER / VARCHAR2)
and returns a booblean indicating if exists a register with the correspondient column having
the same value as the parameter.

In tests, when the input parameter is null, it seems to don't distinguise wich version of EXISTE may execute.
If I convert the parameter to number or char, it does.

Someone knows another more elegant way of doing it instead of casting?

The summary description of the table consulted by the function is:

<b>CREATE TABLE TGEOMUNICIPIOS 
   ( 
 ID NUMBER(*,0), 
 CODINEMUNICIPIO VARCHAR2(11 BYTE)
   );</b>

Insert only one record to prove the issue:

<b> INSERT INTO TGEOMUNICIPIOS VALUES ( 6015, '06015000000' );
 COMMIT;</b>

The package specification and body are:

<b>create or replace PACKAGE PAQ_TGEOMUNICIPIOS
IS
...    
    FUNCTION EXISTE 
    (
    pe_idmunicipio IN TGEOMUNICIPIOS.ID%TYPE
    )
    RETURN BOOLEAN;
    /*
    Devuelve un booleano indicando si existe un municipio con el identificador
    proporcionado. 
    */   

    FUNCTION EXISTE (
    pe_inemunicipio IN TGEOMUNICIPIOS.CODINEMUNICIPIO%TYPE
    )
    RETURN BOOLEAN;
    /*
    Devuelve un booleano indicando si existe un municipio dado su código ine. 
    */  
...
END PAQ_TGEOMUNICIPIOS;

create or replace PACKAGE BODY  PAQ_TGEOMUNICIPIOS
IS
...    
    
    FUNCTION EXISTE 
    (
    pe_idmunicipio IN TGEOMUNICIPIOS.ID%TYPE
    )
    RETURN BOOLEAN
    IS
      v_existe   INTEGER;
    BEGIN
            
      SELECT ID
        INTO v_existe
        FROM TGEOMUNICIPIOS
       WHERE ID = pe_idmunicipio;
    
      RETURN TRUE;
      
    EXCEPTION
    WHEN NO_DATA_FOUND
    THEN
       RETURN FALSE;
         
    END EXISTE;
    

    FUNCTION EXISTE (
    pe_inemunicipio IN TGEOMUNICIPIOS.CODINEMUNICIPIO%TYPE
    )
    RETURN BOOLEAN
    IS
      v_existe  INTEGER;
    BEGIN
    
      SELECT ID
        INTO v_existe
        FROM TGEOMUNICIPIOS
       WHERE CODINEMUNICIPIO LIKE pe_inemunicipio;         
    
      RETURN TRUE;
      
    EXCEPTION
    WHEN OTHERS 
    THEN
       RETURN FALSE;
                
    END EXISTE;
...
END PAQ_TGEOMUNICIPIOS;    </b>

The test code:

<b>DECLARE
BEGIN
   
   --next line doesn't distinguish which version to run
   dbms_output.put_line ( paq_conversiones.f_boolean_a_cadena ( paq_tgeomunicipios.existe ( null ) ) );  
   
   --next line forces to run the first version
   dbms_output.put_line ( paq_conversiones.f_boolean_a_cadena ( paq_tgeomunicipios.existe ( TO_NUMBER( null ) ) ) );  
   
   --next line forces to run the second version
   dbms_output.put_line ( paq_conversiones.f_boolean_a_cadena ( paq_tgeomunicipios.existe ( TO_CHAR( null ) ) ) );

END;   </b>

It returns:

<b>ORA-06550: línea 5, columna 65:
PLS-00307: too many declarations of 'EXISTE' match this call
ORA-06550: línea 5, columna 4:
PL/SQL: Statement ignored
06550. 00000 -  "line %s, column %s:\n%s"
*Cause:    Usually a PL/SQL compilation error.
*Action:</b>

SQL> create or replace
  2  package body pkg is
  3    procedure P(x int) is begin null; end;
  4    procedure P(x varchar2) is begin null; end;
  5  end;
  6  /

Package body created.

SQL>
SQL> exec pkg.p(1);

PL/SQL procedure successfully completed.

SQL> exec pkg.p('1');

PL/SQL procedure successfully completed.

SQL> exec pkg.p(null);
BEGIN pkg.p(null); END;

      *
ERROR at line 1:
ORA-06550: line 1, column 7:
PLS-00307: too many declarations of 'P' match this call
ORA-06550: line 1, column 7:
PL/SQL: Statement ignored

SQL> declare
  2    var int;
  3  begin
  4    pkg.p(var);
  5  end;
  6  /

PL/SQL procedure successfully completed.