unespected Generic parameter 'T' could not be inferred error using generics

testing some code from HakingWithSwift.com

I'd like to make generic extension on FileManager, everything ok with encoding, but I got error with myDecoding func:

Generic parameter 'T' could not be inferred

here how I call those functions

do {
    _ = FileManager.default.MyEncode(fileName: "message.txt", data: "my message")
    }
                
FileManager.default.myDecode(fileName: "message.txt")

here my entire extension

extension FileManager {
    
    
    private func getDocumentsDirectoryPath() -> URL {
        let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
        return paths[0]
    }
    
    
    func MyEncode<T: Codable>(fileName: String, data: T) -> T? {
        let url = getDocumentsDirectoryPath().appendingPathComponent(fileName)
        let encoder = JSONEncoder()
        
        do {
            let encoded = try encoder.encode(data)
            
            do {
                try encoded.write(to: url) 
                do {
                    let input = try String(contentsOf: url)
                        print("letto: \(input)")
                    } catch {
                        print("❌ no imput: \(error.localizedDescription)")
                    }
                
                print("✅ encoded ok")
            } catch {
                print("❌ write failed: \(error.localizedDescription)")
            }
        } catch {
            print("❌ encoded failed: \(error.localizedDescription)")
            
        }
        return nil
    }
    
    func myDecode<T: Codable>(fileName: String) -> T? {
        
        let url = getDocumentsDirectoryPath().appendingPathComponent(fileName)
        let decoder = JSONDecoder()
        
        do {
            let savedData = try Data(contentsOf: url)
            do {
                let decodedData = try decoder.decode(T.self, from: savedData)
                print("✅ decoded ok")
                return decodedData
            } catch {
                print("❌ decoding failed: \(error.localizedDescription)")
            }
        } catch {
            print("❌ no data at url: \(error.localizedDescription)")
        }
        
        return nil
    }
}