Dereferenced pointer in tablesample.c

Hi all,

(Petr in CC)

Coverity is complaining about the following pointer dereference in tablesample_init@tablesample.c:
+               ExprState  *argstate = ExecInitExpr(argexpr, (PlanState *) scanstate);
+
+               if (argstate == NULL)
+               {
+                       fcinfo.argnull[i] = true;
+                       fcinfo.arg[i] = (Datum) 0;;
+               }
+
+               fcinfo.arg[i] = ExecEvalExpr(argstate, econtext,
+                                                                        &fcinfo.argnull[i], NULL);