SQL & PL/SQL

Hi,
we have this code

DECLARE 
    v_cCLOB     CLOB := 'TEST';
    v_cVARCHAR  VARCHAR2(500) := 'TEST';
    v_cCHAR     CHAR(500) := 'TEST';
BEGIN
    
--Trying to get substring beyond the actual amount of text    
--CLOB TEST
    IF NVL(SUBSTR(v_cCLOB, 376, 1), ' ') = ' ' THEN
        dbms_output.put_line('YES');
    ELSE
        dbms_output.put_line('NO');
    END IF;
    
    --VARCHAR TEST
    IF NVL(SUBSTR(v_cVARCHAR, 376, 1), ' ') = ' ' THEN
        dbms_output.put_line('YES');
    ELSE
        dbms_output.put_line('NO');
    END IF;
    
    --CHAR TEST
    IF NVL(SUBSTR(v_cCHAR, 376, 1), ' ') = ' ' THEN
        dbms_output.put_line('YES');
    ELSE
        dbms_output.put_line('NO');
    END IF;    
END;
 

we're expecting to get three YES as the result,
however we got NO, YES, YES for the result

Can we know why we got NO for the CLOB? what is behind the CLOB? Is there any particular value stored there?

thanks