fix: use proper exception type

src/StevanFreeborn.Extensions.Configuration.Secure/Cryptography/StaticKeyProvider.cs

@@ -8,7 +8,7 @@ internal sealed class StaticKeyProvider : IEncryptionKeyProvider
   {
     if (string.IsNullOrWhiteSpace(base64Key))
     {
-      throw new ArgumentNullException(nameof(base64Key));
+      throw new ArgumentException("Cannot be null or whitespace.", nameof(base64Key));
     }
 
     byte[] decodedKey;
@@ -22,7 +22,7 @@ internal sealed class StaticKeyProvider : IEncryptionKeyProvider
       throw new ArgumentException("The provided key is not a valid Base64 string.", nameof(base64Key), ex);
     }
 
-    if (decodedKey.Length != 32)
+    if (decodedKey.Length is not 32)
     {
       throw new ArgumentException("The encryption key must be exactly 32 bytes (256 bits) for AES-256 encryption.", nameof(base64Key));
     }

tests/StevanFreeborn.Extensions.Configuration.Secure.Tests/Unit/Cryptography/StaticKeyProviderTests.cs

@@ -9,7 +9,7 @@ public class StaticKeyProviderTests
   {
     var act = () => new StaticKeyProvider(null!);
 
-    act.Should().Throw<ArgumentNullException>();
+    act.Should().Throw<ArgumentException>();
   }
 
   [Fact]