fixing handling of default values

lib/Doctrine/Import/Builder.php

@@ -221,7 +221,7 @@ END;
 
             $a = array();
 
-            if (isset($column['default']) && $column['default']) {
+            if (isset($column['default'])) {
                 $a[] = '\'default\' => ' . var_export($column['default'], true);
             }
             if (isset($column['notnull']) && $column['notnull']) {
@@ -492,4 +492,4 @@ END;
             throw new Doctrine_Import_Builder_Exception("Couldn't write file " . $options['fileName']);
         }
     }
-}
\ No newline at end of file
+}