[BUG] ZBL and hybrid models do not pass the null UT

[wanghan-iapcm]

Bug summary

ZBL and hybrid models does not pass the testing case of number of neighboring atoms == 0.

DeePMD-kit Version

devel

TensorFlow Version

2.14.0

How did you download the software?

Others (write below)

Input Files, Running Commands, Error Log, etc.

testing case provided by #3391

Steps to Reproduce

comment out the line

deepmd-kit/source/tests/pt/model/test_null_input.py

Line 122 in 89dff77

@unittest.skip("hybrid not supported at the moment")

to reproduce the hybrid issue

comment out the line

deepmd-kit/source/tests/pt/model/test_null_input.py

Line 140 in 89dff77

@unittest.skip("FAILED at the moment")

to reproduce the zbl issue

Further Information, Files, and Links

No response