When using custom BaseTransform in gst-python, pad_template != NULL error occurred

Question

I am developing a custom element using gst-python.
I inherited BaseTransform as shown below, created a custom element, added it to the pipeline, and linked it, but an error occurred.

• Source code:

• Error message:

(<unknown>:56320): GStreamer-Base-CRITICAL **: 15:03:39.106: gst_base_transform_init: assertion 'pad_template != NULL' failed