TypeError: Cannot read properties of undefined (reading 'toUpperCase')

[ghost]

Trying to run on mainnet, installed latest nodejs and yarn, changed RPC in ContextProvider.tsx. Didn't change anything else, but getting the error below when on http://localhost:3000/transmuters after yarn run dev. Will be great if you can help with it (please).

TypeError: Cannot read properties of undefined (reading 'toUpperCase')
  68 | 
  69 |         </div> */}
> 70 |                                                          {process.env.NEXT_PUBLIC_CLUSTER.toUpperCase() === "DEVNET" && <span className="inline-flex items-center px-2.5 py-0.5 rounded-md text-sm font-medium bg-yellow-100 text-yellow-800">Devnet</span>}
     |                                                                                          ^
  71 |                                                          <WalletMultiButton className="btn btn-ghost text-gray-900" />
  72 |                                                  </div>
  73 |                                          </div>

[ghost]

error - src\components\AppBar.tsx (70:41) @ children