Moved the construction of the static "null" strings to stringsGlobals.C which is included in global.Cver to avoid inter-dependency problems in the construction of globals.

Patch supplied by Michael Wild, see
http://openfoam.cfd-online.com/cgi-bin/forum/show.cgi?126/10442

src/OpenFOAM/primitives/strings/stringsGlobals.C

@@ -0,0 +1,45 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     |
+    \\  /    A nd           | Copyright (C) 1991-2008 OpenCFD Ltd.
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+License
+    This file is part of OpenFOAM.
+
+    OpenFOAM is free software; you can redistribute it and/or modify it
+    under the terms of the GNU General Public License as published by the
+    Free Software Foundation; either version 2 of the License, or (at your
+    option) any later version.
+
+    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
+    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+    for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with OpenFOAM; if not, write to the Free Software Foundation,
+    Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
+
+Description
+    Static initializers for
+        Foam::string::null
+        Foam::word::null
+        Foam::fileName::null.
+    This file is included in global.Cver since these members are required by
+    debug.C.
+
+\*---------------------------------------------------------------------------*/
+
+#include "string.H"
+#include "word.H"
+#include "fileName.H"
+
+// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
+
+const Foam::string Foam::string::null;
+const Foam::word Foam::word::null;
+const Foam::fileName Foam::fileName::null;
+
+// ************************************************************************* //