Error lib swift = optional nil

[vincentBoulanger]

* thread #1, queue = 'com.apple.main-thread', stop reason = Swift runtime failure: Unexpectedly found nil while unwrapping an Optional value
    frame #1: 0x0000000104ab5640 mek_stripe_terminal`closure #2 in DiscoverReadersControllerApi.setHandler(arguments=<unavailable>, onCancel=0x0000000104ae56e0 mek_stripe_terminal`partial apply forwarder for implicit closure #4 (mek_stripe_terminal.DiscoveryConfigurationApi) -> Swift.Optional<mek_stripe_terminal.PlatformError> in implicit closure #3 (mek_stripe_terminal.DiscoveryDelegatePlugin) -> (mek_stripe_terminal.DiscoveryConfigurationApi) -> Swift.Optional<mek_stripe_terminal.PlatformError> in mek_stripe_terminal.TerminalPlugin.setupDiscoverReaders() -> () at <compiler-generated>) at TerminalApi.swift:264:24 [opt]
   261 	            let sink = ControllerSink<[ReaderApi]>(events) { $0.map { $0.serialize() } }
   262 	            return onListen(sink, deserializeDiscoveryConfigurationApi(args[0] as! [Any?]))
   263 	        }, { arguments in
-> 264 	            let args = arguments as! [Any?]
    	                       ^
   265 	            return onCancel(deserializeDiscoveryConfigurationApi(args[0] as! [Any?]))
   266 	        }))
   267 	    }
Target 0: (Runner) stopped.

Somebody met this error ?