Make AttractorServer setting nil by default

App/Settings/GeneralSettingsViewController.swift

@@ -169,7 +169,7 @@ class GeneralSettingsViewController: UIViewController
                 cell.contentConfiguration = ButtonContentConfiguration(menu: menu)
             } else if identifier == Self.SyncServerItem {
                 cell.contentConfiguration = TextFieldContentConfiguration(
-                    text: Settings.shared.syncServer,
+                    text: Settings.shared.syncServer ?? "",
                     placeholderText: "https://sync.server.com",
                     textChanged: { newString in
                         Settings.shared.syncServer = newString

App/Settings/Settings.swift

@@ -107,5 +107,22 @@ class Settings
     public var userStylesheet: String = ""
     
     @SettingProperty(key: "syncServer")
-    public var syncServer: String = "https://attractor.severnaya.net"
+    public var syncServer: Optional<String> = "https://attractor.severnaya.net"
+}
+
+extension Optional: RawRepresentable where Wrapped == String
+{
+    public init?(rawValue: String?) {
+        if let rawValue {
+            self = String(rawValue: rawValue)
+        } else {
+            self = .none
+        }
+    }
+    
+    public var rawValue: String? {
+        return self
+    }
+    
+    public typealias RawValue = String?
 }