VS里Add-in开发错误提示GetLayerByName(string lyrName)不是所有的代码都有的代码路径都有返回值怎么改呢？求各位大神帮忙

namespace GIStools
{
    public class search : ESRI.ArcGIS.Desktop.AddIns.Tool
    {

        private IApplication m_application;
        private static IMap map;
 
        public search()
        {
        }

        protected override void OnUpdate()
        {
             Enabled = ArcMap.Application != null;
        }
         public static ILayer GetLayerByName(string lyrName)
        {
             ILayer findLayer = null;
            IEnumLayer pEnumLayer = map.get_Layers();
             pEnumLayer.Reset();
             ILayer pLayer = pEnumLayer.Next();
             while (pLayer != null)
            {
                 if (pLayer.Name == lyrName)
                 {
                     findLayer = pLayer;
                }
               pLayer = pEnumLayer.Next();
                    return findLayer;
       }
            
        }
    }
}