[Koha] Software errror - Can't call biblio on an undefined value

Hi Ian getting the below error when I open a member record and it is happening only for few records; Software error: Can't call biblio on an undefined value at /use/share/koha/lib/c4/members.pm line 767 Koha version 17.11 on Ubuntu mariadb. This error is not there in koha 16.05 for the same record. Pls help me how to resolve the error. Regards Suresh kumar