[libxml++] Document: Test for nullptr in a constructor

[Kjell Ahlstedt <kjellahl src gnome org>]

commit fa1ca3e3a02d78edcd0269fe9cde629af9a9af27
Author: Kjell Ahlstedt <kjell ahlstedt bredband net>
Date:   Thu Jan 7 09:54:14 2016 +0100

    Document: Test for nullptr in a constructor
    
    In Document(_xmlDoc* doc), throw an exception if doc==nullptr.

 libxml++/document.cc |    3 +++
 libxml++/document.h  |    1 +
 2 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/libxml++/document.cc b/libxml++/document.cc
index be1ed2f..acd1fe3 100644
--- a/libxml++/document.cc
+++ b/libxml++/document.cc
@@ -179,6 +179,9 @@ Document::Document(const Glib::ustring& version)
 Document::Document(xmlDoc* doc)
   : impl_(doc)
 {
+  if (!impl_)
+    throw internal_error("xmlDoc pointer cannot be nullptr");
+
   impl_->_private = this;
 }
 
diff --git a/libxml++/document.h b/libxml++/document.h
index 90ffaa4..5d4ba60 100644
--- a/libxml++/document.h
+++ b/libxml++/document.h
@@ -85,6 +85,7 @@ public:
    * The created xmlpp::Document takes ownership of the xmlDoc.
    * When the Document is deleted, so is the xmlDoc and all its nodes.
    * @param doc A pointer to an xmlDoc struct. Must not be <tt>nullptr</tt>.
+   * @throws xmlpp::internal_error If @a doc is <tt>nullptr</tt>.
    */
   explicit Document(_xmlDoc* doc);