Prevent unnecessary fill value writing.

src/cdf_int.c

@@ -202,10 +202,15 @@ cdf_def_var(int ncid, const char *name, nc_type xtype, int ndims, const int dimi
 void
 cdf_def_var_serial(int ncid, const char *name, nc_type xtype, int ndims, const int dimids[], int *varidp)
 {
-  const int status = nc_def_var(ncid, name, xtype, ndims, dimids, varidp);
-
+  int status = nc_def_var(ncid, name, xtype, ndims, dimids, varidp);
   if (CDF_Debug || status != NC_NOERR) Message("ncid=%d  name=%s  xtype=%d  ndims=%d  varid=%d", ncid, name, xtype, ndims, *varidp);
-
+  if (status == NC_NOERR)
+    {
+      int fileFormat;
+      status = nc_inq_format(ncid, &fileFormat);
+      if (status == NC_NOERR && (fileFormat == NC_FORMAT_NETCDF4 || fileFormat == NC_FORMAT_NETCDF4_CLASSIC))
+        status = nc_def_var_fill(ncid, *varidp, 1, NULL);
+    }
   if (status != NC_NOERR) Error("%s", nc_strerror(status));
 }