Implement ContractAnnotation for IsNullOrEmpty & IsNullOrWhiteSpace extension methods.

framework/src/Volo.Abp.Core/System/AbpStringExtensions.cs

@@ -46,6 +46,7 @@ public static class AbpStringExtensions
     /// <summary>
     /// Indicates whether this string is null or an System.String.Empty string.
     /// </summary>
+    [ContractAnnotation("str:null => true")]
     public static bool IsNullOrEmpty(this string str)
     {
         return string.IsNullOrEmpty(str);
@@ -54,6 +55,7 @@ public static class AbpStringExtensions
     /// <summary>
     /// indicates whether this string is null, empty, or consists only of white-space characters.
     /// </summary>
+    [ContractAnnotation("str:null => true")]
     public static bool IsNullOrWhiteSpace(this string str)
     {
         return string.IsNullOrWhiteSpace(str);

framework/src/Volo.Abp.Core/System/Collections/Generic/AbpCollectionExtensions.cs

@@ -12,6 +12,7 @@ public static class AbpCollectionExtensions
     /// <summary>
     /// Checks whatever given collection object is null or has no item.
     /// </summary>
+    [ContractAnnotation("source:null => true")]
     public static bool IsNullOrEmpty<T>([CanBeNull] this ICollection<T> source)
     {
         return source == null || source.Count <= 0;