EDIT

Especially for Person.lifespan_end and Person.lifespan_start the problem existed. See #9081

UPDATE AgentBase 
SET lifespan_start = NULL, lifespan_end = NULL
WHERE lifespan_start = '00000000' && lifespan_end = '00000000'

better split the command but these seem to appear always together.

Also check for occurrence in other TimePeriod usages.

Further classes are:

• InstitutionalMembership.period
• !! EventBase.timeperiod
  • Amplification.
  • DerivationEvent
  • DeterminationEvent
  • GatheringEvent
  • SingleRead
  • MaterialOrMethodEvent.
• DescriptionElementBase.timeperiod
• DescriptionElementBase.period (for TermporalData)
• DefinedTermBase.validPeriod (for NamedArea)
• Media.mediaCreated
• Reference.datePublished
• Classification.timeperiod