Check if the connection is not null or already closed

src/main/java/fr/xephi/authme/datasource/SQLite.java

@@ -350,7 +350,8 @@ public class SQLite implements DataSource {
     @Override
     public synchronized void close() {
         try {
-            con.close();
+        	if (con != null && !con.isClosed())
+        		con.close();
         } catch (SQLException ex) {
             logSqlException(ex);
         }