printer json BUGFIX indentation for "null" metadata

Signed-off-by: Igor Ryzhov <iryzhov@nfware.com>
diff --git a/src/printer_json.c b/src/printer_json.c
index eabb56c..c94a765 100644
--- a/src/printer_json.c
+++ b/src/printer_json.c
@@ -868,7 +868,7 @@
             LEVEL_DEC;
             ly_print_(pctx->out, "%s%*s}", DO_FORMAT ? "\n" : "", INDENT);
         } else {
-            ly_print_(pctx->out, "null");
+            ly_print_(pctx->out, "%*snull", INDENT);
         }
         LEVEL_PRINTED;
         if (!matching_node(iter, iter->next)) {