diff --git a/src/Reveal.Sdk.Dom.Tests/Core/Utilities/RdashDocumentValidatorFixture.cs b/src/Reveal.Sdk.Dom.Tests/Core/Utilities/RdashDocumentValidatorFixture.cs
index b3d9c923..ea46dce8 100644
--- a/src/Reveal.Sdk.Dom.Tests/Core/Utilities/RdashDocumentValidatorFixture.cs
+++ b/src/Reveal.Sdk.Dom.Tests/Core/Utilities/RdashDocumentValidatorFixture.cs
@@ -80,18 +80,44 @@ public void Validate_Adds_Fields()
             var document = new RdashDocument();
             document.Visualizations.Add(new GridVisualization(dataSourceItem));
 
-            Assert.Empty(document.Visualizations[0].DataDefinition.AsTabular().Fields);
-
             RdashDocumentValidator.Validate(document);
 
             Assert.Single(document.Visualizations[0].DataDefinition.AsTabular().Fields);
         }
 
+        [Fact]
+        public void Validate_ThrowsException_When_Fields_Are_Null()
+        {
+            var dataSourceItem = new DataSourceItem("Test", new DataSource());
+            dataSourceItem.Fields = null;
+
+            var document = new RdashDocument();
+            document.Visualizations.Add(new GridVisualization(dataSourceItem));
+
+            var exception = Assert.Throws<Exception>(() => RdashDocumentValidator.Validate(document));
+
+            Assert.Equal("Fields for DataSourceItem Test is null or empty.", exception.Message);
+        }
+
+        [Fact]
+        public void Validate_ThrowsException_When_Fields_Are_Empty()
+        {
+            var dataSourceItem = new DataSourceItem("Test", new DataSource()).SetFields(new List<IField>());
+
+            var document = new RdashDocument();
+            document.Visualizations.Add(new GridVisualization(dataSourceItem));
+
+            var exception = Assert.Throws<Exception>(() => RdashDocumentValidator.Validate(document));
+
+            Assert.Equal("Fields for DataSourceItem Test is null or empty.", exception.Message);
+        }
+
         [Fact]
         public void Validate_PreventsDuplicate_Fields()
         {
             var dataSourceItem = new DataSourceItem("Test", new DataSource()).SetFields(new List<IField>
             {
+                new TextField("Test"),
                 new TextField("Test"),
                 new TextField("Test")
             });
@@ -99,8 +125,6 @@ public void Validate_PreventsDuplicate_Fields()
             var document = new RdashDocument();
             document.Visualizations.Add(new GridVisualization(dataSourceItem));
 
-            Assert.Empty(document.Visualizations[0].DataDefinition.AsTabular().Fields);
-
             RdashDocumentValidator.Validate(document);
 
             Assert.Single(document.Visualizations[0].DataDefinition.AsTabular().Fields);
diff --git a/src/Reveal.Sdk.Dom/Core/Utilities/RdashDocumentValidator.cs b/src/Reveal.Sdk.Dom/Core/Utilities/RdashDocumentValidator.cs
index be8acaa1..99dd10d1 100644
--- a/src/Reveal.Sdk.Dom/Core/Utilities/RdashDocumentValidator.cs
+++ b/src/Reveal.Sdk.Dom/Core/Utilities/RdashDocumentValidator.cs
@@ -36,27 +36,15 @@ static void FixVisualizations(RdashDocument document)
 
         private static void FixFields(TabularDataDefinition tdd)
         {
-            if (tdd.DataSourceItem.Fields?.Count != 0)
-            {
-                // Create a HashSet to track added field names
-                HashSet<string> fieldNames = new HashSet<string>(tdd.Fields.Select(f => f.FieldName));
-
-                foreach (var field in tdd.DataSourceItem.Fields.Clone())
-                {
-                    if (field == null)
-                        throw new Exception($"Field for DataSourceItem {tdd.DataSourceItem.Title} is null.");
+            if (tdd.Fields?.Count == 0)
+                throw new Exception($"Fields for DataSourceItem {tdd.DataSourceItem.Title} is null or empty.");
 
-                    //prevent adding duplicate fields
-                    if (!fieldNames.Contains(field.FieldName))
-                    {
-                        tdd.Fields.Add(field);
-                        fieldNames.Add(field.FieldName);
-                    }
-                }
+            // Check if there are duplicates
+            var hasDuplicates = tdd.Fields.GroupBy(f => f.FieldName).Any(g => g.Count() > 1);
+            if (hasDuplicates)
+            {
+                tdd.Fields = tdd.Fields.GroupBy(f => f.FieldName).Select(g => g.First()).ToList();
             }
-
-            if (tdd.Fields?.Count == 0)
-                throw new Exception($"Fields for DataSourceItem {tdd.DataSourceItem.Title} is null.");
         }
 
         static void FixJoinedTables(TabularDataDefinition tdd)