Why FF pickup NULL instead the value

Summary

FF doesn't pick up correctly value

Content

Hello,

we have the FF :

INPUTS ARE DATA_ELEMENTS (TEXT_TEXT)

L_LOCAL = ' '
L_RETURN = ' '

 IF DATA_ELEMENTS.EXISTS('PERSON_ID')THEN
 (
   L_LOCAL = DATA_ELEMENTS['PERSON_ID']
   L_RETURN = GET_VALUE_SET('XXHR_COA_DETAILS', '|=P_PERSON_ID='''||L_LOCAL||'''')
)

RULE_VALUE = L_RETURN

RETURN RULE_VALUE

with the Value set of the image attached.

 

I replicate the query of the value set into 

SELECT 
ppa.****_attribute14
from per_all_assignments_m ppa
where 
ppa.assignment_type = 'E'
  and trunc(sysdate) between ppa.effective_start_date and ppa.effective_end_date