exp init: --explicit not working

[dberenbaum]

Bug Report

Description

dvc exp init --explicit fails.

Reproduce

In a fresh dvc repo:

$ dvc exp init -v --explicit echo foo
2021-11-02 12:16:19,313 ERROR: unexpected error - 'live'
------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/dave/Code/dvc/dvc/main.py", line 55, in main
    ret = cmd.do_run()
  File "/Users/dave/Code/dvc/dvc/command/base.py", line 45, in do_run
    return self.run()
  File "/Users/dave/Code/dvc/dvc/command/experiments.py", line 841, in run
    initialized_stage = init(
  File "/Users/dave/Code/dvc/dvc/repo/experiments/init.py", line 221, in init
    defaults.pop("live")  # suppress live otherwise
KeyError: 'live'
------------------------------------------------------------
2021-11-02 12:16:19,405 DEBUG: Version info for developers:
DVC version: 2.8.3.dev13+g5690015e
---------------------------------
Platform: Python 3.9.5 on macOS-12.0.1-arm64-arm-64bit
Supports:
        webhdfs (fsspec = 2021.9.0),
        http (aiohttp = 3.7.4.post0, aiohttp-retry = 2.4.5),
        https (aiohttp = 3.7.4.post0, aiohttp-retry = 2.4.5),
        s3 (s3fs = 2021.8.0, boto3 = 1.17.5)
Cache types: <https://error.dvc.org/no-dvc-cache>
Caches: local
Remotes: local
Workspace directory: apfs on /dev/disk3s1s1
Repo: dvc, git

Having any troubles? Hit us up at https://dvc.org/support, we are always happy to help!
2021-11-02 12:16:19,406 DEBUG: Analytics is disabled.

Environment information

DVC version: 2.8.3.dev13+g5690015e