Can I omit the username when searching for LDAP Group Memberships with Spring Security's DefaultLdapAuthoritiesPopulator?

Question

I am relatively new to LDAP and would like to know if I can omit the username parameter when calling getGroupMembershipRoles on DefaultLdapAuthoritiesPopulator without experiencing any disadvantages (link to the documentation).

public Set<GrantedAuthority> getGroupMembershipRoles(String userDn, String username) {
    if (getGroupSearchBase() == null) {
        return new HashSet<>();
    }
    Set<GrantedAuthority> authorities = new HashSet<>();
    logger.trace(LogMessage.of(() -> "Searching for roles for user " + username + " with DN " + userDn
                                     + " and filter " + this.groupSearchFilter + " in search base " + getGroupSearchBase()));
    Set<Map<String, List<String>>> userRoles = getLdapTemplate().searchForMultipleAttributeValues(
            getGroupSearchBase(), this.groupSearchFilter, new String[] { userDn, username },
            new String[] { this.groupRoleAttribute });
    logger.debug(LogMessage.of(() -> "Found roles from search " + userRoles));
    for (Map<String, List<String>> role : userRoles) {
        GrantedAuthority authority = this.authorityMapper.apply(role);
        if (authority != null) {
            authorities.add(authority);
        }
    }
    return authorities;
}

Both userDn and username are then passed to searchForMultipleAttributeValues on SpringSecurityLdapTemplate (link to documentation).

public Set<Map<String, List<String>>> searchForMultipleAttributeValues(String base, String filter, Object[] params, String[] attributeNames) {
    // Escape the params acording to RFC2254
    Object[] encodedParams = new String[params.length];
    for (int i = 0; i < params.length; i++) {
        encodedParams[i] = LdapEncoder.filterEncode(params[i].toString());
    }
    String formattedFilter = MessageFormat.format(filter, encodedParams);
    logger.trace(LogMessage.format("Using filter: %s", formattedFilter));
    HashSet<Map<String, List<String>>> result = new HashSet<>();
    ContextMapper roleMapper = (ctx) -> {
        DirContextAdapter adapter = (DirContextAdapter) ctx;
        Map<String, List<String>> record = new HashMap<>();
        if (ObjectUtils.isEmpty(attributeNames)) {
            try {
                for (NamingEnumeration enumeration = adapter.getAttributes().getAll(); enumeration.hasMore();) {
                    Attribute attr = (Attribute) enumeration.next();
                    extractStringAttributeValues(adapter, record, attr.getID());
                }
            }
            catch (NamingException ex) {
                org.springframework.ldap.support.LdapUtils.convertLdapException(ex);
            }
        }
        else {
            for (String attributeName : attributeNames) {
                extractStringAttributeValues(adapter, record, attributeName);
            }
        }
        record.put(DN_KEY, Arrays.asList(getAdapterDN(adapter)));
        result.add(record);
        return null;
    };
    SearchControls ctls = new SearchControls();
    ctls.setSearchScope(this.searchControls.getSearchScope());
    ctls.setReturningAttributes((attributeNames != null && attributeNames.length > 0) ? attributeNames : null);
    search(base, formattedFilter, ctls, roleMapper);
    return result;
}

However, if I pass an empty string for username I still get all groups where the user is registered with his dn. It seems that the username is not absolutely necessary. Why is it requested by Spring Security anyway? And can I safely omit it without expecting unwanted side effects?

Many thanks for any information