I can't actually see this module:

$ ls -l /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_*
-rw-r--r-- 1 root root 203014 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_conntrack.ko
-rw-r--r-- 1 root root  10518 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_conntrack_amanda.ko
-rw-r--r-- 1 root root   5070 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_conntrack_broadcast.ko
-rw-r--r-- 1 root root  26230 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_conntrack_ftp.ko
-rw-r--r-- 1 root root 100054 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_conntrack_h323.ko
-rw-r--r-- 1 root root  15934 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_conntrack_irc.ko
-rw-r--r-- 1 root root   6694 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_conntrack_netbios_ns.ko
-rw-r--r-- 1 root root  56158 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_conntrack_netlink.ko
-rw-r--r-- 1 root root  26334 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_conntrack_pptp.ko
-rw-r--r-- 1 root root  17062 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_conntrack_proto_gre.ko
-rw-r--r-- 1 root root  13446 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_conntrack_sane.ko
-rw-r--r-- 1 root root  41318 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_conntrack_sip.ko
-rw-r--r-- 1 root root   7238 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_conntrack_snmp.ko
-rw-r--r-- 1 root root  13726 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_conntrack_tftp.ko
-rw-r--r-- 1 root root   5294 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_dup_netdev.ko
-rw-r--r-- 1 root root  10214 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_log_common.ko
-rw-r--r-- 1 root root   6670 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_log_netdev.ko
-rw-r--r-- 1 root root  34838 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_nat.ko
-rw-r--r-- 1 root root   7054 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_nat_amanda.ko
-rw-r--r-- 1 root root   9390 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_nat_ftp.ko
-rw-r--r-- 1 root root   8734 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_nat_irc.ko
-rw-r--r-- 1 root root   6102 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_nat_redirect.ko
-rw-r--r-- 1 root root  17438 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_nat_sip.ko
-rw-r--r-- 1 root root   6022 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_nat_tftp.ko
-rw-r--r-- 1 root root  13662 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_synproxy_core.ko
-rw-r--r-- 1 root root 125414 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_tables.ko
-rw-r--r-- 1 root root   7854 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_tables_inet.ko
-rw-r--r-- 1 root root   9862 May  6 16:59 /lib/modules/4.15.0-50-generic/kernel/net/netfilter/nf_tables_netdev.ko