A discharge of contract comes to an end in four ways: Performance ,Agreement ,Breach ,Frustration

what way is the case below discharge by? I tried to did a summary

APCO CONSTRUCTION INC vs ZITTING CONSTRUCTION,INC. FACTS OF THE CASE. APCO Construction was the general contractor on a Las Vegas construction project that came to a halt in 2008.APCO subcontracted wood-framing, sheathing, and shimming work to Zitting Construction. The subcontract did state that the payment to Zitting was on the condition of APCO's receipt of payment from the project owner, Gemstone, basically known as "A pay-if-paid clause." Zitting's went to court claiming a lawsuit that it was owed $750,000 for works that it had done which did include retainage and change order work. APCO had never received payment from the owner, and defended itself against the Zitting claim based on the subcontract's pay-if-paid clause.

DECISIONS BY THE COURTS. The trial court granted a summary judgment in favor of Zitting stating that the pay-if-paid provisions were void and unenforceable under Nevada law. An appeal was lodged in the Nevada Supreme Court and it conquered with the trial court, but it did emphasize that pay-if-paid clauses are not unenforceable in Nevada per see. It stated that the courts ought to consider whether the subcontract payment provision in question complies with or violated the specific terms of a Nevada statute establishing payment rights of subcontractors. The Nevada Supreme Court came to a conclusion that the pay-if-paid provision were unenforceable, under a specified statute, as the clause which limited Zitting's right to prompt payment.

the case: https://www.ejcdc.org/enforceability-of-pay-if-paid-clauses-under-nevada-law-apco-construction-inc-v-zitting-brothers-construction-inc-supreme-court-of-nevada-2020-by-hugh-anderson/

plz tell me if the case is related to discharge of contact, if yes, what is it discharge by?