1.9.0 breaking firestore unit tests

[busunkim96]

https://github.com/googleapis/python-firestore/blob/master/google/cloud/firestore_v1/types/document.py

busunkim@busunkim:~/github/python-firestore$ nox -s unit-3.8
nox > Running session unit-3.8
nox > Creating virtual environment (virtualenv) using python3.8 in .nox/unit-3-8
nox > pip install pytest-asyncio aiounittest
nox > pip install mock pytest pytest-cov
nox > pip install -e .
nox > pip install proto-plus==1.9.0
nox > py.test --quiet --cov=google.cloud.firestore --cov=google.cloud --cov=tests.unit --cov-append --cov-config=.coveragerc --cov-report= --cov-fail-under=0 tests/unit
Coverage.py warning: Module google.cloud.firestore was never imported. (module-not-imported)
Coverage.py warning: Module google.cloud was previously imported, but not measured (module-not-measured)

================================================================================= ERRORS ==================================================================================
___________________________________________________ ERROR collecting tests/unit/gapic/firestore_v1/test_firestore_v1.py ___________________________________________________
tests/unit/gapic/firestore_v1/test_firestore_v1.py:35: in <module>
    from google.cloud.firestore_v1.services.firestore import FirestoreAsyncClient
google/cloud/firestore_v1/__init__.py:25: in <module>
    from google.cloud.firestore_v1 import types
google/cloud/firestore_v1/types/__init__.py:23: in <module>
    from .document import (
google/cloud/firestore_v1/types/document.py:95: in <module>
    class Value(proto.Message):
.nox/unit-3-8/lib/python3.8/site-packages/proto/message.py:139: in __new__
    field.descriptor.oneof_index = oneofs[field.oneof]
.nox/unit-3-8/lib/python3.8/site-packages/proto/fields.py:96: in descriptor
    type_name = self.enum._meta.full_name
.nox/unit-3-8/lib/python3.8/site-packages/google/protobuf/internal/enum_type_wrapper.py:114: in __getattr__
    raise AttributeError('Enum {} has no value defined for name {!r}'.format(
E   AttributeError: Enum NullValue has no value defined for name '_meta'
______________________________________________________________ ERROR collecting tests/unit/v1/test_order.py _______________________________________________________________
tests/unit/v1/test_order.py:19: in <module>
    from google.cloud.firestore_v1._helpers import encode_value, GeoPoint
google/cloud/firestore_v1/__init__.py:25: in <module>
    from google.cloud.firestore_v1 import types
google/cloud/firestore_v1/types/__init__.py:23: in <module>
    from .document import (
google/cloud/firestore_v1/types/document.py:95: in <module>
    class Value(proto.Message):
.nox/unit-3-8/lib/python3.8/site-packages/proto/message.py:139: in __new__
    field.descriptor.oneof_index = oneofs[field.oneof]
.nox/unit-3-8/lib/python3.8/site-packages/proto/fields.py:96: in descriptor
    type_name = self.enum._meta.full_name
.nox/unit-3-8/lib/python3.8/site-packages/google/protobuf/internal/enum_type_wrapper.py:114: in __getattr__
    raise AttributeError('Enum {} has no value defined for name {!r}'.format(
E   AttributeError: Enum NullValue has no value defined for name '_meta'
______________________________________________________________ ERROR collecting tests/unit/v1/test_watch.py _______________________________________________________________
tests/unit/v1/test_watch.py:18: in <module>
    from google.cloud.firestore_v1.types import firestore
google/cloud/firestore_v1/__init__.py:25: in <module>
    from google.cloud.firestore_v1 import types
google/cloud/firestore_v1/types/__init__.py:23: in <module>
    from .document import (
google/cloud/firestore_v1/types/document.py:95: in <module>
    class Value(proto.Message):
.nox/unit-3-8/lib/python3.8/site-packages/proto/message.py:139: in __new__
    field.descriptor.oneof_index = oneofs[field.oneof]
.nox/unit-3-8/lib/python3.8/site-packages/proto/fields.py:96: in descriptor
    type_name = self.enum._meta.full_name
.nox/unit-3-8/lib/python3.8/site-packages/google/protobuf/internal/enum_type_wrapper.py:114: in __getattr__
    raise AttributeError('Enum {} has no value defined for name {!r}'.format(
E   AttributeError: Enum NullValue has no value defined for name '_meta'


========================================================================= short test summary info =========================================================================
ERROR tests/unit/gapic/firestore_v1/test_firestore_v1.py - AttributeError: Enum NullValue has no value defined for name '_meta'
ERROR tests/unit/v1/test_order.py - AttributeError: Enum NullValue has no value defined for name '_meta'
ERROR tests/unit/v1/test_watch.py - AttributeError: Enum NullValue has no value defined for name '_meta'
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Interrupted: 3 errors during collection !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
3 errors in 4.04s
nox > Command py.test --quiet --cov=google.cloud.firestore --cov=google.cloud --cov=tests.unit --cov-append --cov-config=.coveragerc --cov-report= --cov-fail-under=0 tests/unit failed with exit code 2
nox > Session unit-3.8 failed.