DependencyService.Get<ILogManager>().GetLog() System.NullReferenceException: 'Object reference not set to an instance of an object' - xamarin.forms

Question

I am trying to execute Xamarin App.
I can build and deploy solutions on both Android and iOS devices. But when I am Debugging/running iOS App I am receiving an error
**System.NullReferenceException:** 'Object reference not set to an instance of an object'
on
private static ILogger logger = DependencyService.Get<ILogManager>().GetLog(); line
I have installed the latest version of the Nlog NuGet Package.
My ILogManager file is
namespace VolMobile.AppData.Interfaces
{
public interface ILogManager
{
ILogger GetLog([System.Runtime.CompilerServices.CallerFilePath]string callerFilePath = "");
void Reload();
void DeleteLog();
}
}
How can I resolve this issue?
update
My NLogManager iOS file
using System;
using System.Collections.Generic;
using Xamarin.Forms;
using System.IO;
using NLog;
using NLog.Config;
using NLog.Targets;
using VolMobile.AppData.Interfaces;
using VolMobile.iOS.Logging;
[assembly: Dependency(typeof(NLogManager))]
namespace VolMobile.iOS.Logging
{
public class NLogManager : ILogManager
{
string logFile;
LoggingConfiguration config;
public NLogManager()
{
Reload();
}
public void Reload()
{
config = new LoggingConfiguration();
var consoleTarget = new ConsoleTarget();
config.AddTarget("console", consoleTarget);
var consoleRule = new LoggingRule("*", LogLevel.Trace, consoleTarget);
config.LoggingRules.Add(consoleRule);
//File logging level
LogLevel llSetting = LogLevel.Off;
IEnumerable<LogLevel> sysLevels = LogLevel.AllLevels;
//default to trace at startup
string currentLogLevel = "Trace";
//load the app state if available
if (App.AppState != null)
currentLogLevel = App.AppState.AppSettings.LogLevel;// AppData.AppData.LogLevel;
foreach (LogLevel ll in sysLevels)
{
if (currentLogLevel == ll.Name)
{
llSetting = ll;
}
}
var fileTarget = new FileTarget();
string folder = System.Environment.GetFolderPath(System.Environment.SpecialFolder.MyDocuments); //android.os.environment is the other option
fileTarget.FileName = Path.Combine(folder, "Log.txt");
fileTarget.Layout = "${longdate}|${level:uppercase=true}|${callsite}|${appdomain}|${logger}|${threadid}|${message}|{exception:format=tostring}";
config.AddTarget("file", fileTarget);
logFile = Path.Combine(folder, "Log.txt");
var fileRule = new LoggingRule("*", llSetting, fileTarget);//LogLevel.Warn
config.LoggingRules.Add(fileRule);
LogManager.Configuration = config;
}
public void DeleteLog()
{
File.Delete(logFile);
}
// Services.Logging.ILogger
//AppData.Interfaces.ILogger
//public NLogLogger GetLog([System.Runtime.CompilerServices.CallerFilePath] string callerFilePath = "")
//{
// string fileName = callerFilePath;
// if (fileName.Contains("/"))
// {
// fileName = fileName.Substring(fileName.LastIndexOf("/", StringComparison.CurrentCultureIgnoreCase) + 1);
// }
// var logger = LogManager.GetLogger(fileName);
// return new NLogLogger(logger, logFile);
//}
public AppData.Interfaces.ILogger GetLog([System.Runtime.CompilerServices.CallerFilePath] string callerFilePath = "")
{
string fileName = callerFilePath;
if (fileName.Contains("/"))
{
fileName = fileName.Substring(fileName.LastIndexOf("/", StringComparison.CurrentCultureIgnoreCase) + 1);
}
var logger = LogManager.GetLogger(fileName);
return new NLogLogger(logger, logFile);
}
}
}
The app is working perfectly fine on iOS, Andriod simulators, and Android Device only not on iOS devices.