get_all_versions fails if one doc isn't readable

[amoeba]

> get_all_versions(env$mn, "doi:10.18739/A2NQ09")
Your login certificate is missing or unreadable. You must login again via CILogon using 'dataone::downloadCert(CertificateManager())'
Attempting to call as public user without being authenticated.
Your login certificate is missing or unreadable. You must login again via CILogon using 'dataone::downloadCert(CertificateManager())'
Attempting to call as public user without being authenticated.
Your login certificate is missing or unreadable. You must login again via CILogon using 'dataone::downloadCert(CertificateManager())'
Attempting to call as public user without being authenticated.
Your login certificate is missing or unreadable. You must login again via CILogon using 'dataone::downloadCert(CertificateManager())'
Attempting to call as public user without being authenticated.
Error in get_chain_neighbors(mn, pid) : 
  trying to get slot "obsoletes" from an object of a basic class ("NULL") with no slots
In addition: Warning message:
In .local(x, ...) :
  Error getting SystemMetadata: READ not allowed on urn:uuid:49295b90-d47c-447a-bdb2-2809b1240971

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