消除平台模块warning

common/Tnb.Common/Extension/StringExtensions.cs

@@ -345,7 +345,7 @@ public static class StringExtensions
     /// 指示指定的字符串是 null 或者 System.String.Empty 字符串.
     /// </summary>
     [DebuggerStepThrough]
-    public static bool IsNullOrEmpty(this string value)
+    public static bool IsNullOrEmpty(this string? value)
     {
         return string.IsNullOrEmpty(value);
     }
@@ -363,7 +363,7 @@ public static class StringExtensions
     /// 指示指定的字符串是 null、空或者仅由空白字符组成.
     /// </summary>
     [DebuggerStepThrough]
-    public static bool IsMissing(this string value)
+    public static bool IsMissing(this string? value)
     {
         return string.IsNullOrWhiteSpace(value);
     }