hotdoc generation fail on rtp-doc

I'm trying to update my gst-build setup but I get this error:

subprojects/gst-plugins-good/docs/meson.build:78:4: ERROR:  Tried to create target "rtp-doc", but a target of that name already exists. 

I hacked this just to get it build:

diff --git a/docs/meson.build b/docs/meson.build
index 17cc4c19d5..ec9b41984a 100644
--- a/docs/meson.build
+++ b/docs/meson.build
@@ -67,7 +67,7 @@ import sys
 import json
 
 with open("@0@") as f:
-    print(':'.join(json.load(f).keys()), end='')
+    print(':_'.join(json.load(f).keys()), end='')
 '''.format(plugins_cache))
 
 assert(list_plugin_res.returncode() == 0,