A quote from my law textbook

[brin_bellway]

The maximum duration of a lease, in contrast, must be definite. It therefore is impossible to create a lease that would last “until the Maple Leafs next win the Cup.”³⁰

30. The maximum duration must be definite, but a tenancy may end earlier. Therefore, it would be possible to have a lease “for 999 years or until the Maple Leafs next win the Cup.” It is enough that the lease is certain to end within 999 years, even though there is a slim chance that it will end earlier.

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(I'm not sure if this would be *more* or *less* funny if I had any previous knowledge of the Maple Leafs' reputation.)