diff --git a/src/Pipedrive.net/Converters/CustomFieldConverter.cs b/src/Pipedrive.net/Converters/CustomFieldConverter.cs
index 0edbce8d..ccfe5d55 100644
--- a/src/Pipedrive.net/Converters/CustomFieldConverter.cs
+++ b/src/Pipedrive.net/Converters/CustomFieldConverter.cs
@@ -181,6 +181,11 @@ public override void WriteJson(JsonWriter writer, object value, JsonSerializer s
                 var property_name = property.PropertyName;
                 var property_value = property.ValueProvider.GetValue(value);
 
+                if(property.NullValueHandling == NullValueHandling.Ignore && property_value == null)
+                {
+                    continue;
+                }
+
                 writer.WritePropertyName(property_name);
                 if (property.Converter != null && property.Converter.CanWrite)
                 {
diff --git a/src/Pipedrive.net/Models/Request/Deals/DealUpdate.cs b/src/Pipedrive.net/Models/Request/Deals/DealUpdate.cs
index aacee82f..40ce603e 100644
--- a/src/Pipedrive.net/Models/Request/Deals/DealUpdate.cs
+++ b/src/Pipedrive.net/Models/Request/Deals/DealUpdate.cs
@@ -9,56 +9,56 @@ namespace Pipedrive
     [JsonConverter(typeof(CustomFieldConverter))]
     public class DealUpdate : IEntityWithCustomFields
     {
-        [JsonProperty("title")]
+        [JsonProperty("title",  NullValueHandling=NullValueHandling.Ignore)]
         public string Title { get; set; }
 
-        [JsonProperty("value")]
+        [JsonProperty("value",  NullValueHandling=NullValueHandling.Ignore)]
         public decimal? Value { get; set; }
 
-        [JsonProperty("currency")]
+        [JsonProperty("currency",  NullValueHandling=NullValueHandling.Ignore)]
         public string Currency { get; set; }
 
-        [JsonProperty("user_id")]
+        [JsonProperty("user_id",  NullValueHandling=NullValueHandling.Ignore)]
         public long? UserId { get; set; }
 
-        [JsonProperty("person_id")]
+        [JsonProperty("person_id",  NullValueHandling=NullValueHandling.Ignore)]
         public long? PersonId { get; set; }
 
-        [JsonProperty("org_id")]
+        [JsonProperty("org_id",  NullValueHandling=NullValueHandling.Ignore)]
         public long? OrgId { get; set; }
 
-        [JsonProperty("stage_id")]
+        [JsonProperty("stage_id",  NullValueHandling=NullValueHandling.Ignore)]
         public long? StageId { get; set; }
 
-        [JsonProperty("status")]
+        [JsonProperty("status",  NullValueHandling=NullValueHandling.Ignore)]
         [JsonConverter(typeof(StringEnumConverter))]
         public DealStatus? Status { get; set; }
 
-        [JsonProperty("probability")]
+        [JsonProperty("probability",  NullValueHandling=NullValueHandling.Ignore)]
         public double? Probability { get; set; }
 
-        [JsonProperty("lost_reason")]
+        [JsonProperty("lost_reason",  NullValueHandling=NullValueHandling.Ignore)]
         public string LostReason { get; set; }
 
-        [JsonProperty("visible_to")]
-        public Visibility VisibleTo { get; set; }
+        [JsonProperty("visible_to",  NullValueHandling=NullValueHandling.Ignore)]
+        public Visibility? VisibleTo { get; set; }
 
-        [JsonProperty("add_time")]
+        [JsonProperty("add_time",  NullValueHandling=NullValueHandling.Ignore)]
         public DateTime? AddTime { get; set; }
 
-        [JsonProperty("close_time")]
+        [JsonProperty("close_time",  NullValueHandling=NullValueHandling.Ignore)]
         public DateTime? CloseTime { get; set; }
 
-        [JsonProperty("lost_time")]
+        [JsonProperty("lost_time",  NullValueHandling=NullValueHandling.Ignore)]
         public DateTime? LostTime { get; set; }
 
-        [JsonProperty("first_won_time")]
+        [JsonProperty("first_won_time",  NullValueHandling=NullValueHandling.Ignore)]
         public DateTime? FirstWonTime { get; set; }
 
-        [JsonProperty("won_time")]
+        [JsonProperty("won_time",  NullValueHandling=NullValueHandling.Ignore)]
         public DateTime? WonTime { get; set; }
 
-        [JsonProperty("expected_close_date")]
+        [JsonProperty("expected_close_date",  NullValueHandling=NullValueHandling.Ignore)]
         public DateTime? ExpectedCloseDate { get; set; }
 
         [JsonIgnore]