Did Tenant Waive Landlord's Duty to Mitigate Damages?

A restaurant tenant isn’t happy about what it deems to be the landlord’s inadequate efforts to market the mall and abandons the property. Instead of immediately seeking a replacement, the landlord lets the space remain vacant and sues the tenant for rent.

We didn’t default on the lease, the tenant insists. And even if we did, we shouldn’t be on the hook for full rent payments because the landlord didn’t take steps to mitigate its damages.