diff --git a/src/Kiota.Builder/Extensions/OpenApiSchemaExtensions.cs b/src/Kiota.Builder/Extensions/OpenApiSchemaExtensions.cs
index 9e834047d5..7d316743e1 100644
--- a/src/Kiota.Builder/Extensions/OpenApiSchemaExtensions.cs
+++ b/src/Kiota.Builder/Extensions/OpenApiSchemaExtensions.cs
@@ -34,21 +34,21 @@ public static string GetSchemaTitle(this OpenApiSchema schema) {
         public static IEnumerable<string> GetSchemaReferenceIds(this OpenApiSchema schema, HashSet<OpenApiSchema> visitedSchemas = null) {
             if(visitedSchemas == null)
                 visitedSchemas = new();            
-            if(!visitedSchemas.Contains(schema)) {
+            if(schema != null && !visitedSchemas.Contains(schema)) {
                 visitedSchemas.Add(schema);
                 var result = new List<string>();
                 if(!string.IsNullOrEmpty(schema.Reference?.Id))
                     result.Add(schema.Reference.Id);
                 if(!string.IsNullOrEmpty(schema.Items?.Reference?.Id))
                     result.Add(schema.Items.Reference.Id);
-                if(schema.Properties != null)
-                    result.AddRange(schema.Properties.Values.SelectMany(x => x.GetSchemaReferenceIds(visitedSchemas)));
-                if(schema.AnyOf != null)
-                    result.AddRange(schema.AnyOf.SelectMany(x => x.GetSchemaReferenceIds(visitedSchemas)));
-                if(schema.AllOf != null)
-                    result.AddRange(schema.AllOf.SelectMany(x => x.GetSchemaReferenceIds(visitedSchemas)));
-                if(schema.OneOf != null)
-                    result.AddRange(schema.OneOf.SelectMany(x => x.GetSchemaReferenceIds(visitedSchemas)));
+                var subSchemaReferences = (schema.Properties?.Values ?? Enumerable.Empty<OpenApiSchema>())
+                                            .Union(schema.AnyOf ?? Enumerable.Empty<OpenApiSchema>())
+                                            .Union(schema.AllOf ?? Enumerable.Empty<OpenApiSchema>())
+                                            .Union(schema.OneOf ?? Enumerable.Empty<OpenApiSchema>())
+                                            .SelectMany(x => x.GetSchemaReferenceIds(visitedSchemas))
+                                            .ToList();// this to list is important otherwise the any marks the schemas as visited and add range doesn't find anything
+                if(subSchemaReferences.Any())
+                    result.AddRange(subSchemaReferences);
                 return result;
             } else 
                 return Enumerable.Empty<string>();
diff --git a/tests/Kiota.Builder.Tests/Extensions/OpenApiSchemaExtensionsTests.cs b/tests/Kiota.Builder.Tests/Extensions/OpenApiSchemaExtensionsTests.cs
index 69d94cf5b4..8fd7ac0f5d 100644
--- a/tests/Kiota.Builder.Tests/Extensions/OpenApiSchemaExtensionsTests.cs
+++ b/tests/Kiota.Builder.Tests/Extensions/OpenApiSchemaExtensionsTests.cs
@@ -5,6 +5,30 @@
 
 namespace Kiota.Builder.Extensions.Tests {
     public class OpenApiSchemaExtensionsTests {
+        [Fact]
+        public void Defensive() {
+            Assert.Empty(OpenApiSchemaExtensions.GetSchemaReferenceIds(null));
+            var schema = new OpenApiSchema{
+                AnyOf = null
+            };
+            Assert.Null(schema.AnyOf);
+            Assert.Empty(schema.GetSchemaReferenceIds());
+            schema = new() {
+                AllOf = null
+            };
+            Assert.Null(schema.AllOf);
+            Assert.Empty(schema.GetSchemaReferenceIds());
+            schema = new() {
+                OneOf = null
+            };
+            Assert.Null(schema.OneOf);
+            Assert.Empty(schema.GetSchemaReferenceIds());
+            schema = new() {
+                Properties = null
+            };
+            Assert.Null(schema.Properties);
+            Assert.Empty(schema.GetSchemaReferenceIds());
+        }
         [Fact]
         public void GetSchemaTitleAllOf() {
             var schema = new OpenApiSchema {
@@ -18,8 +42,8 @@ public void GetSchemaTitleAllOf() {
                 }
             };
             var names = schema.GetSchemaTitles();
-            Assert.Equal("microsoft.graph.entity", names.First());
-            Assert.Equal("microsoft.graph.user", names.Last());
+            Assert.Contains("microsoft.graph.entity", names);
+            Assert.Contains("microsoft.graph.user", names);
             Assert.Equal("microsoft.graph.user", schema.GetSchemaTitle());
         }
         [Fact]
@@ -39,8 +63,8 @@ public void GetSchemaTitleAllOfNested() {
                 }
             };
             var names = schema.GetSchemaTitles();
-            Assert.Equal("microsoft.graph.entity", names.First());
-            Assert.Equal("microsoft.graph.user", names.Last());
+            Assert.Contains("microsoft.graph.entity", names);
+            Assert.Contains("microsoft.graph.user", names);
             Assert.Equal("microsoft.graph.user", schema.GetSchemaTitle());
         }
         [Fact]
@@ -56,8 +80,8 @@ public void GetSchemaTitleAnyOf() {
                 }
             };
             var names = schema.GetSchemaTitles();
-            Assert.Equal("microsoft.graph.entity", names.First());
-            Assert.Equal("microsoft.graph.user", names.Last());
+            Assert.Contains("microsoft.graph.entity", names);
+            Assert.Contains("microsoft.graph.user", names);
             Assert.Equal("microsoft.graph.user", schema.GetSchemaTitle());
         }
         [Fact]
@@ -73,8 +97,8 @@ public void GetSchemaTitleOneOf() {
                 }
             };
             var names = schema.GetSchemaTitles();
-            Assert.Equal("microsoft.graph.entity", names.First());
-            Assert.Equal("microsoft.graph.user", names.Last());
+            Assert.Contains("microsoft.graph.entity", names);
+            Assert.Contains("microsoft.graph.user", names);
             Assert.Equal("microsoft.graph.user", schema.GetSchemaTitle());
         }
         [Fact]
@@ -85,7 +109,7 @@ public void GetSchemaTitleItems() {
                 },
             };
             var names = schema.GetSchemaTitles();
-            Assert.Equal("microsoft.graph.entity", names.First());
+            Assert.Contains("microsoft.graph.entity", names);
             Assert.Equal("microsoft.graph.entity", schema.GetSchemaTitle());
             Assert.Single(names);
         }
@@ -95,7 +119,7 @@ public void GetSchemaTitleTitle() {
                 Title = "microsoft.graph.entity"
             };
             var names = schema.GetSchemaTitles();
-            Assert.Equal("microsoft.graph.entity", names.First());
+            Assert.Contains("microsoft.graph.entity", names);
             Assert.Equal("microsoft.graph.entity", schema.GetSchemaTitle());
             Assert.Single(names);
         }
@@ -124,8 +148,8 @@ public void GetReferenceIdsAllOf() {
                 }
             };
             var names = schema.GetSchemaReferenceIds();
-            Assert.Equal("microsoft.graph.entity", names.First());
-            Assert.Equal("microsoft.graph.user", names.Last());
+            Assert.Contains("microsoft.graph.entity", names);
+            Assert.Contains("microsoft.graph.user", names);
         }
         [Fact]
         public void GetReferenceIdsAllOfNested() {
@@ -148,8 +172,8 @@ public void GetReferenceIdsAllOfNested() {
                 }
             };
             var names = schema.GetSchemaReferenceIds();
-            Assert.Equal("microsoft.graph.entity", names.First());
-            Assert.Equal("microsoft.graph.user", names.Last());
+            Assert.Contains("microsoft.graph.entity", names);
+            Assert.Contains("microsoft.graph.user", names);
         }
         [Fact]
         public void GetReferenceIdsAnyOf() {
@@ -168,8 +192,8 @@ public void GetReferenceIdsAnyOf() {
                 }
             };
             var names = schema.GetSchemaReferenceIds();
-            Assert.Equal("microsoft.graph.entity", names.First());
-            Assert.Equal("microsoft.graph.user", names.Last());
+            Assert.Contains("microsoft.graph.entity", names);
+            Assert.Contains("microsoft.graph.user", names);
         }
         [Fact]
         public void GetReferenceIdsOneOf() {
@@ -188,8 +212,8 @@ public void GetReferenceIdsOneOf() {
                 }
             };
             var names = schema.GetSchemaReferenceIds();
-            Assert.Equal("microsoft.graph.entity", names.First());
-            Assert.Equal("microsoft.graph.user", names.Last());
+            Assert.Contains("microsoft.graph.entity", names);
+            Assert.Contains("microsoft.graph.user", names);
         }
         [Fact]
         public void GetReferenceIdsItems() {
@@ -201,7 +225,7 @@ public void GetReferenceIdsItems() {
                 },
             };
             var names = schema.GetSchemaReferenceIds();
-            Assert.Equal("microsoft.graph.entity", names.First());
+            Assert.Contains("microsoft.graph.entity", names);
             Assert.Single(names);
         }
         [Fact]
@@ -212,7 +236,7 @@ public void GetReferenceIdsTitle() {
                 }
             };
             var names = schema.GetSchemaReferenceIds();
-            Assert.Equal("microsoft.graph.entity", names.First());
+            Assert.Contains("microsoft.graph.entity", names);
             Assert.Single(names);
         }
         [Fact]