NFSv4: Check for NULL argument in nfs_*_seqid() functions

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
diff --git a/fs/nfs/nfs4xdr.c b/fs/nfs/nfs4xdr.c
index 7e7be5a..d05fada 100644
--- a/fs/nfs/nfs4xdr.c
+++ b/fs/nfs/nfs4xdr.c
@@ -946,7 +946,10 @@
 static void encode_nfs4_seqid(struct xdr_stream *xdr,
 		const struct nfs_seqid *seqid)
 {
-	encode_uint32(xdr, seqid->sequence->counter);
+	if (seqid != NULL)
+		encode_uint32(xdr, seqid->sequence->counter);
+	else
+		encode_uint32(xdr, 0);
 }
 
 static void encode_compound_hdr(struct xdr_stream *xdr,