diff --git a/src/Plaid.OpenApiParser/Program.cs b/src/Plaid.OpenApiParser/Program.cs
index 7bd72f66..4e7c0bce 100644
--- a/src/Plaid.OpenApiParser/Program.cs
+++ b/src/Plaid.OpenApiParser/Program.cs
@@ -328,8 +328,11 @@ private static string GetPropertyType(string className, string propertyName, Ope
 		{
 			if (schema.Reference.Id.EndsWith("Nullable"))
 			{
-				var realType = schema.AllOf.First();
-				return GetPropertyType(className, propertyName, realType, entityType);
+				if (schema.AllOf.Count > 0)
+				{
+					var realType = schema.AllOf.First();
+					return GetPropertyType(className, propertyName, realType, entityType);
+				}
 			}
 			else if (schema.AdditionalProperties != null)
 				return $"IReadOnlyDictionary<string, {GetPropertyType(className, propertyName, schema.AdditionalProperties, type)}>";