Prevent AttributeError during get_certificate_version

sdk/keyvault/azure-keyvault-certificates/CHANGELOG.md

@@ -1,6 +1,7 @@
 # Release History
 
 ## 4.2.0b2 (Unreleased)
+- Fixed an `AttributeError` during `get_certificate_version`
 - Values of `x-ms-keyvault-region` and `x-ms-keyvault-service-version` headers
   are no longer redacted in logging output.
 - Updated minimum `azure-core` version to 1.4.0

sdk/keyvault/azure-keyvault-certificates/azure/keyvault/certificates/_models.py

@@ -320,11 +320,17 @@ def _from_certificate_bundle(cls, certificate_bundle):
         # type: (models.CertificateBundle) -> KeyVaultCertificate
         """Construct a certificate from an autorest-generated certificateBundle"""
         # pylint:disable=protected-access
+
+        if certificate_bundle.policy:
+            policy = CertificatePolicy._from_certificate_policy_bundle(certificate_bundle.policy)
+        else:
+            policy = None
+
         return cls(
             properties=CertificateProperties._from_certificate_item(certificate_bundle),
             key_id=certificate_bundle.kid,
             secret_id=certificate_bundle.sid,
-            policy=CertificatePolicy._from_certificate_policy_bundle(certificate_bundle.policy),
+            policy=policy,
             cer=certificate_bundle.cer,
         )