endOfDataMark in BKConfiguration can be set to nil

Source/BKCentral.swift

@@ -314,12 +314,13 @@ public class BKCentral: BKPeer, BKCBCentralManagerStateDelegate, BKConnectionPoo
         }
     }
 
-    internal override func sendData(_ data: Data, toRemotePeer remotePeer: BKRemotePeer) -> Bool {
+    internal override func sendData(_ data: Data?, toRemotePeer remotePeer: BKRemotePeer) -> Bool {
         guard let remotePeripheral = remotePeer as? BKRemotePeripheral,
                 let peripheral = remotePeripheral.peripheral,
                 let characteristic = remotePeripheral.characteristicData else {
             return false
         }
+        guard let data = data else { return true }
         peripheral.writeValue(data, for: characteristic, type: .withoutResponse)
         return true
     }

Source/BKConfiguration.swift

@@ -39,7 +39,7 @@ public class BKConfiguration {
     public var dataServiceCharacteristicUUID: CBUUID
 
     /// Data used to indicate that no more data is coming when communicating.
-    public var endOfDataMark: Data
+    public var endOfDataMark: Data?
 
     /// Data used to indicate that a transfer was cancellen when communicating.
     public var dataCancelledMark: Data

Source/BKPeer.swift

@@ -100,7 +100,7 @@ public class BKPeer {
         }
     }
 
-    internal func sendData(_ data: Data, toRemotePeer remotePeer: BKRemotePeer) -> Bool {
+    internal func sendData(_ data: Data?, toRemotePeer remotePeer: BKRemotePeer) -> Bool {
         fatalError("Function must be overridden by subclass")
     }
 

Source/BKPeripheral.swift

@@ -160,10 +160,11 @@ public class BKPeripheral: BKPeer, BKCBPeripheralManagerDelegate, BKAvailability
         }
     }
 
-    internal override func sendData(_ data: Data, toRemotePeer remotePeer: BKRemotePeer) -> Bool {
+    internal override func sendData(_ data: Data?, toRemotePeer remotePeer: BKRemotePeer) -> Bool {
         guard let remoteCentral = remotePeer as? BKRemoteCentral else {
             return false
         }
+        guard let data = data else { return true }
         return peripheralManager.updateValue(data, for: characteristicData, onSubscribedCentrals: [ remoteCentral.central ])
     }
 

Source/BKRemotePeer.swift

@@ -56,7 +56,11 @@ public class BKRemotePeer: Equatable {
     }
 
     internal func handleReceivedData(_ receivedData: Data) {
-        if receivedData == configuration!.endOfDataMark {
+        guard let endOfDataMark = configuration!.endOfDataMark else {
+            delegate?.remotePeer(self, didSendArbitraryData: receivedData)
+            return
+        }
+        if receivedData == endOfDataMark {
             if let finalData = data {
                 delegate?.remotePeer(self, didSendArbitraryData: finalData)
             }