fix: [stix import] Avoiding issue with test_mechanisms with no rule value
fix: [stix import] Avoiding issue with test_mechanisms with no rule value

MISP/MISP,MISP/MISP,SteveClement/MISP,SteveClement/MISP,SteveClement/MISP,SteveClement/MISP,MISP/MISP,MISP/MISP,SteveClement/MISP,MISP/MISP