Fix possible NullPointerException in RdfMap.close(). (#667)

Author: blackwinter

metafix/src/main/java/org/metafacture/metafix/maps/RdfMap.java

@@ -398,7 +398,10 @@ private String read(final String url) throws IOException {
     @Override
     public void close() {
         map.clear();
-        model.close();
+
+        if (model != null) {
+            model.close();
+        }
     }
 
     private enum Select {

metamorph/src/main/java/org/metafacture/metamorph/maps/FileMap.java

@@ -296,4 +296,5 @@ public void close() throws IOException {
         map.clear();
         fileOpener.closeStream();
     }
+
 }