to vitiate the policy

[rus]

...the policy or policies of insurance shall not have been vitiated by the LESSEE or payment of the policy monies withheld in whole or in part in consequence of some act or default of the LESSEE, his employees or agents, ...

[V]

to vitiate - от "vice", порок.
Приводить к недействительности
создавать порок

нужен пошире контекст

[rus]

вот, пжалуста, контекст пошире:

"If the whole or any part of the DEMISED PREMISES shall at any time be destroyed or damaged, or the BUILDING damaged rendering the DEMISED PREMISES inaccessible, by any of the INSURED RISKS or due to the LESSOR’s fault so as to render the DEMISED PREMISES unfit for occupation or use or inaccessible and, in case it has happened due to the INSURED RISKS, the policy or policies of insurance shall not have been vitiated by the LESSEE or payment of the policy monies withheld in whole or in part in consequence of some act or default of the LESSEE, his employees or agents, then the RENT, the DUE PROPORTION of the SERVICE CHARGE and the OUTGOINGS payable under this LEASE or a fair proportion of them according to the nature and extent of the damage sustained shall cease until the DEMISED PREMISES shall be rendered fit for occupation or use or accessible again."

[Irisha]

Думаю так: ... при условии, что Арендатор не совершал действий, которые могли бы привести к недействительности страхового полиса (страховых полисов)...

[rus]

Irisha, спасибо большое за Ваше мнение!