Hi all.I am facing an issue with Liferay 7.1

I have a Liferay 7.1 which is connected to an LDAP.I am trying to access to LDAP attributes but I am not able to do it. In previous versions of Liferay, I used PortalLdapUtil, but it is no longer available.
I trying adding this to my class:
@Reference(
            policy = ReferencePolicy.DYNAMIC,
            policyOption = ReferencePolicyOption.GREEDY
        )
    private volatile PortalLDAP _portalLDAP;
    
    
but _portalLDAP is always null.
Can anyone give me ideas? I would appreciate any help.
​​​​​​​Thanks in advance