gst-xmllaunch-0.8 adder.xml
RUNNING pipeline ...
ERROR: from element /pipeline0/sinesrc0: Internal GStreamer error: negotiation
problem.  File a bug.
ERROR: from element /pipeline0/adder0: Internal GStreamer error: pad problem.
File a bug.
Additional debug info:
gstpad.c(3392): gst_pad_pull: /pipeline0/adder0:
NULL buffer during pull on adder0:sink0
Execution ended after 1 iterations (sum 16926000 ns, average
        16926000 ns, min 16926000 ns, max 16926000
        ns).

** ERROR **: file gstoptimalscheduler.c: line 871
        (destroy_group): assertion failed: (group->group_links ==
        NULL)
aborting...
Aborted