infer rootKey and fixed lint errors

Author: portellaa

Sources/XMLCoder/Encoder/XMLEncoder.swift

@@ -324,7 +324,10 @@ open class XMLEncoder {
     /// floating-point value is encountered during encoding, and the encoding
     /// strategy is `.throw`.
     /// - throws: An error if any value throws an error during encoding.
-    open func encode<T: Encodable>(_ value: T, withRootKey rootKey: String, rootAttributes: [String : String], header: XMLHeader? = nil) throws -> Data {
+    open func encode<T: Encodable>(_ value: T,
+                                   withRootKey rootKey: String? = nil,
+                                   rootAttributes: [String: String],
+                                   header: XMLHeader? = nil) throws -> Data {
         let encoder = XMLEncoderImplementation(
             options: options,
             nodeEncodings: []
@@ -335,6 +338,8 @@ open class XMLEncoder {
         let attributes = rootAttributes.map(Attribute.init)
 
         let elementOrNone: XMLCoderElement?
+        
+        let rootKey = rootKey ?? "\(T.self)"
 
         if let keyedBox = topLevel as? KeyedBox {
             elementOrNone = XMLCoderElement(key: rootKey, box: keyedBox, attributes: attributes)