conda index gives a KeyError: timestamp

[mcs07]

Actual Behavior

conda index gives a KeyError:

conda index
Traceback (most recent call last):
  File "/opt/anaconda/bin/conda-index", line 11, in <module>
    sys.exit(main())
  File "/opt/anaconda/lib/python3.7/site-packages/conda_build/cli/main_index.py", line 91, in main
    return execute(sys.argv[1:])
  File "/opt/anaconda/lib/python3.7/site-packages/conda_build/cli/main_index.py", line 87, in execute
    current_index_versions=args.current_index_versions_file)
  File "/opt/anaconda/lib/python3.7/site-packages/conda_build/api.py", line 401, in update_index
    subdirs=ensure_list(subdir), current_index_versions=current_index_versions)
  File "/opt/anaconda/lib/python3.7/site-packages/conda_build/index.py", line 312, in update_index
    current_index_versions=current_index_versions)
  File "/opt/anaconda/lib/python3.7/site-packages/conda_build/index.py", line 857, in index
    self._update_channeldata(channel_data, patched_repodata, subdir)
  File "/opt/anaconda/lib/python3.7/site-packages/conda_build/index.py", line 1258, in _update_channeldata
    for pkg_name, pkg_tuples in package_groups.items()]
  File "/opt/anaconda/lib/python3.7/site-packages/conda_build/index.py", line 1258, in <listcomp>
    for pkg_name, pkg_tuples in package_groups.items()]
  File "/opt/anaconda/lib/python3.7/site-packages/conda_build/index.py", line 1257, in <lambda>
    package_groups = [next(iter(sorted(pkg_tuples, key=lambda x: x[1]['timestamp'])))
KeyError: 'timestamp'

Expected Behavior

Successful conda index.

Steps to Reproduce

Run conda index with conda-build v3.18.3.

No problem with conda-build v3.18.2. Could be related to #3528?

Output of conda info

     active environment : None
            shell level : 0
       user config file : /root/.condarc
 populated config files : /opt/anaconda/.condarc
                          /root/.condarc
          conda version : 4.6.14
    conda-build version : 3.18.3
         python version : 3.7.3.final.0
       base environment : /opt/anaconda  (writable)
           channel URLs : <private channel>/linux-64
                          <private channel>/noarch
                          https://conda.anaconda.org/conda-forge/linux-64
                          https://conda.anaconda.org/conda-forge/noarch
                          https://conda.anaconda.org/schrodinger/linux-64
                          https://conda.anaconda.org/schrodinger/noarch
                          https://repo.anaconda.com/pkgs/main/linux-64
                          https://repo.anaconda.com/pkgs/main/noarch
                          https://repo.anaconda.com/pkgs/free/linux-64
                          https://repo.anaconda.com/pkgs/free/noarch
                          https://repo.anaconda.com/pkgs/r/linux-64
                          https://repo.anaconda.com/pkgs/r/noarch
          package cache : /opt/anaconda/pkgs
                          /root/.conda/pkgs
       envs directories : /opt/anaconda/envs
                          /root/.conda/envs
               platform : linux-64
             user-agent : conda/4.6.14 requests/2.22.0 CPython/3.7.3 Linux/3.13.0-147-generic ubuntu/14.04.6 glibc/2.19
                UID:GID : 0:0
             netrc file : None
           offline mode : False

[github-actions]

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