diff --git a/Makefile b/Makefile
index 50efe37..23bf763 100644
--- a/Makefile
+++ b/Makefile
@@ -14,7 +14,7 @@ gen-buggy:
 	dotnet run --project OpenApiGen -- Examples/OpenApiGen.config.json Examples/BuggyApi.json generated
 
 gen-invest:
-	dotnet run --project OpenApiGen -- Examples/OpenApiGen.config.json Examples/InvestApi.json generated
+	dotnet run --project OpenApiGen -- Examples/InvestApi.config.json Examples/InvestApi.json generated
 
 gen-art:
 	dotnet run --project OpenApiGen -- Examples/FundApi.config.json Examples/ArtApi.json generated
diff --git a/OpenApiGen/Generators/TypeScriptAxiosGenerator.cs b/OpenApiGen/Generators/TypeScriptAxiosGenerator.cs
index 730dc40..9305121 100644
--- a/OpenApiGen/Generators/TypeScriptAxiosGenerator.cs
+++ b/OpenApiGen/Generators/TypeScriptAxiosGenerator.cs
@@ -1,4 +1,3 @@
-using System.Data.Common;
 using System.Text;
 using System.Text.RegularExpressions;
 
@@ -175,14 +174,6 @@ private string ParameterPrototype(Parameter param) {
         return $"{param.Name}{optional}: {tsType}";
     }
 
-    private static string ParameterQuery(Parameter param, int index) {
-        if (param.Schema.Default is null) {
-            return $"${{{param.Name} ? `&{param.Name}=${{encodeURIComponent({param.Name})}}` : ''}}";
-        } else {
-            return $"&{param.Name}=${{encodeURIComponent({param.Name} ?? {param.Schema.Default})}}";
-        }
-    }
-
     private static string ParameterQueryInitializer(Parameter param) {
         return $"if ({param.Name} !== undefined) __query__.push(`{param.Name}=${{encodeURIComponent({param.Name})}}`);";
     }
@@ -266,16 +257,23 @@ private string RawGenerateType(int indent, Schema schema, string[] composedRequi
             sb.Append('}');
             return sb.ToString();
         } else if (schema is EnumSchema enumSchema) {
-            return string.Join(" | ", enumSchema.Enum.Select(e => $"\"{e}\""));
+            return string.Join(" | ", enumSchema.Enum.Where(e => e is not null).Select(e => $"\"{e}\""));
         } else if (schema is PrimitiveSchema primSchema) {
-            return (primSchema.Type, primSchema.Format) switch {
+            var types =
+                (primSchema.Types, primSchema.Type) switch {
+                    (string[], _) => primSchema.Types,
+                    (null, string) => [primSchema.Type],
+                    _ => ["void"]
+                };
+            return string.Join(" | ", types.Select(type => (type, primSchema.Format) switch {
                 ("string", "binary") => "File",
                 ("string", _) => "string",
                 ("integer", _) => "number",
                 ("number", _) => "number",
                 ("boolean", _) => "boolean",
+                ("null", _) => "null",
                 _ => "void"
-            };
+            }));
         } else {
             throw new ApplicationException("Unknown schema type.");
         }
diff --git a/OpenApiGen/OpenApiDef.cs b/OpenApiGen/OpenApiDef.cs
index 025fb18..ee27895 100644
--- a/OpenApiGen/OpenApiDef.cs
+++ b/OpenApiGen/OpenApiDef.cs
@@ -70,12 +70,12 @@ public record Parameter {
 
 [JsonConverter(typeof(SchemaConverter))]
 public abstract record Schema {
-    public bool? Nullable { get; init; }
+    public bool? Nullable { get; init; } // deprecated in 3.1
     public object? Default { get; init; }
 }
 
 public sealed record EnumSchema : Schema {
-    public required List<string> Enum { get; init; }
+    public required List<string?> Enum { get; init; }
 }
 
 public sealed record RefSchema : Schema {
@@ -105,5 +105,5 @@ public sealed record Discriminator {
 public sealed record PrimitiveSchema : Schema {
     public string? Type { get; init; }   // "string", "integer", "number", "boolean"
     public string? Format { get; init; } // "date-time", "uuid", etc.
+    public string[]? Types { get; init; } // new in 3.1
 }
-