Refactor null checks with 'is not null' in JwtBuilder

To better follow the naming convention and improve code readability, the null checks in JwtBuilder.cs have been updated from 'is object' to 'is not null'. The updated null checks include the variables '_algorithm', '_algFactory', '_validator', '_jsonSerializerFactory', '_urlEncoder', and '_jwt.Payload'.

src/JWT/Builder/JwtBuilder.cs

@@ -348,9 +348,9 @@ private void TryCreateEncoder()
             if (_urlEncoder is null)
                 throw new InvalidOperationException($"Can't instantiate {nameof(JwtEncoder)}. Call {nameof(WithUrlEncoder)}.");
 
-            if (_algorithm is object)
+            if (_algorithm is not null)
                 _encoder = new JwtEncoder(_algorithm, jsonSerializer, _urlEncoder);
-            else if (_algFactory is object)
+            else if (_algFactory is not null)
                 _encoder = new JwtEncoder(_algFactory, jsonSerializer, _urlEncoder);
         }
 
@@ -364,9 +364,9 @@ private void TryCreateDecoder()
             if (_urlEncoder is null)
                 throw new InvalidOperationException($"Can't instantiate {nameof(JwtDecoder)}. Call {nameof(WithUrlEncoder)}.");
 
-            if (_algorithm is object)
+            if (_algorithm is not null)
                 _decoder = new JwtDecoder(jsonSerializer, _validator, _urlEncoder, _algorithm);
-            else if (_algFactory is object)
+            else if (_algFactory is not null)
                 _decoder = new JwtDecoder(jsonSerializer, _validator, _urlEncoder, _algFactory);
             else if (!_valParams.ValidateSignature)
                 _decoder = new JwtDecoder(jsonSerializer, _urlEncoder);
@@ -385,7 +385,7 @@ private void TryCreateDecoderForHeader()
 
         private void TryCreateValidator()
         {
-            if (_validator is object)
+            if (_validator is not null)
                 return;
 
             var jsonSerializer = _jsonSerializerFactory.Create();
@@ -445,10 +445,10 @@ private void EnsureCanDecodeHeader()
         /// Checks whether enough dependencies were supplied to encode a new token.
         /// </summary>
         private bool CanEncode() =>
-            (_algorithm is object || _algFactory is object) &&
-            _jsonSerializerFactory is object &&
-            _urlEncoder is object &&
-            _jwt.Payload is object;
+            (_algorithm is not null || _algFactory is not null) &&
+            _jsonSerializerFactory is not null &&
+            _urlEncoder is not null &&
+            _jwt.Payload is not null;
 
         /// <summary>
         /// Checks whether enough dependencies were supplied to decode a token.
@@ -459,7 +459,7 @@ private bool CanDecode()
                 return false;
 
             if (_valParams.ValidateSignature)
-                return _validator is object && (_algorithm is object || _algFactory is object);
+                return _validator is not null && (_algorithm is not null || _algFactory is not null);
 
             return true;
         }
@@ -469,10 +469,7 @@ private bool CanDecodeHeader()
             if (_urlEncoder is null)
                 return false;
 
-            if (_jsonSerializerFactory is null)
-                return false;
-
-            return true;
+            return _jsonSerializerFactory is not null;
         }
 
         private string GetPropName(MemberInfo prop)