diff --git a/checker/internal/type_checker_impl.cc b/checker/internal/type_checker_impl.cc
index 7b05e1cb9..0967c7326 100644
--- a/checker/internal/type_checker_impl.cc
+++ b/checker/internal/type_checker_impl.cc
@@ -180,7 +180,7 @@ absl::StatusOr<AstType> FlattenType(const Type& type) {
     case TypeKind::kError:
       return AstType(ast_internal::ErrorType());
     case TypeKind::kNull:
-      return AstType(nullptr);
+      return AstType(ast_internal::NullType());
     case TypeKind::kBool:
       return AstType(ast_internal::PrimitiveType::kBool);
     case TypeKind::kInt:
diff --git a/checker/internal/type_checker_impl_test.cc b/checker/internal/type_checker_impl_test.cc
index 208861030..66fb7b57c 100644
--- a/checker/internal/type_checker_impl_test.cc
+++ b/checker/internal/type_checker_impl_test.cc
@@ -926,7 +926,7 @@ INSTANTIATE_TEST_SUITE_P(
     ::testing::Values(
         AstTypeConversionTestCase{
             .decl_type = NullType(),
-            .expected_type = AstType(nullptr),
+            .expected_type = AstType(ast_internal::NullType()),
         },
         AstTypeConversionTestCase{
             .decl_type = DynType(),
diff --git a/codelab/BUILD b/codelab/BUILD
index 954ec25ba..7cc3e6767 100644
--- a/codelab/BUILD
+++ b/codelab/BUILD
@@ -39,6 +39,10 @@ cc_library(
     name = "exercise1",
     srcs = ["exercise1.cc"],
     hdrs = ["exercise1.h"],
+    tags = [
+        "manual",
+        "nobuilder",
+    ],
     deps = [
         "//eval/public:activation",
         "//eval/public:builtin_func_registrar",
diff --git a/common/ast/expr.h b/common/ast/expr.h
index f23eafdad..a3820c4a6 100644
--- a/common/ast/expr.h
+++ b/common/ast/expr.h
@@ -17,7 +17,6 @@
 #ifndef THIRD_PARTY_CEL_CPP_BASE_AST_INTERNAL_EXPR_H_
 #define THIRD_PARTY_CEL_CPP_BASE_AST_INTERNAL_EXPR_H_
 
-#include <cstddef>
 #include <cstdint>
 #include <memory>
 #include <string>
@@ -33,19 +32,6 @@
 
 namespace cel::ast_internal {
 
-// Temporary aliases that will be deleted in future.
-using NullValue = std::nullptr_t;
-using Bytes = cel::BytesConstant;
-using Constant = cel::Constant;
-using ConstantKind = cel::ConstantKind;
-using Ident = cel::IdentExpr;
-using Expr = cel::Expr;
-using ExprKind = cel::ExprKind;
-using Select = cel::SelectExpr;
-using Call = cel::CallExpr;
-using CreateList = cel::ListExpr;
-using CreateStruct = cel::StructExpr;
-using Comprehension = cel::ComprehensionExpr;
 
 // An extension that was requested for the source expression.
 class Extension {
@@ -566,10 +552,17 @@ enum class ErrorType { kErrorTypeValue = 0 };
 
 struct UnspecifiedType : public absl::monostate {};
 
-struct DynamicType : public absl::monostate {};
+struct DynamicType {};
+
+inline bool operator==(const DynamicType&, const DynamicType&) { return true; }
+inline bool operator!=(const DynamicType&, const DynamicType&) { return false; }
+
+struct NullType {};
+inline bool operator==(const NullType&, const NullType&) { return true; }
+inline bool operator!=(const NullType&, const NullType&) { return false; }
 
 using TypeKind =
-    absl::variant<UnspecifiedType, DynamicType, NullValue, PrimitiveType,
+    absl::variant<UnspecifiedType, DynamicType, NullType, PrimitiveType,
                   PrimitiveTypeWrapper, WellKnownType, ListType, MapType,
                   FunctionType, MessageType, ParamType,
                   absl_nullable std::unique_ptr<Type>, ErrorType, AbstractType>;
@@ -599,7 +592,7 @@ class Type {
   }
 
   bool has_null() const {
-    return absl::holds_alternative<NullValue>(type_kind_);
+    return absl::holds_alternative<NullType>(type_kind_);
   }
 
   bool has_primitive() const {
@@ -646,12 +639,12 @@ class Type {
     return absl::holds_alternative<AbstractType>(type_kind_);
   }
 
-  NullValue null() const {
-    auto* value = absl::get_if<NullValue>(&type_kind_);
+  NullType null() const {
+    auto* value = absl::get_if<NullType>(&type_kind_);
     if (value != nullptr) {
       return *value;
     }
-    return nullptr;
+    return {};
   }
 
   PrimitiveType primitive() const {
diff --git a/common/ast/expr_test.cc b/common/ast/expr_test.cc
index 2ef74488a..fb62cbda7 100644
--- a/common/ast/expr_test.cc
+++ b/common/ast/expr_test.cc
@@ -81,7 +81,7 @@ TEST(AstTest, FunctionTypeDefaults) {
 }
 
 TEST(AstTest, TypeDefaults) {
-  EXPECT_EQ(Type().null(), nullptr);
+  EXPECT_EQ(Type().null(), NullType());
   EXPECT_EQ(Type().primitive(), PrimitiveType::kPrimitiveTypeUnspecified);
   EXPECT_EQ(Type().wrapper(), PrimitiveType::kPrimitiveTypeUnspecified);
   EXPECT_EQ(Type().well_known(), WellKnownType::kWellKnownTypeUnspecified);
diff --git a/common/ast_proto.cc b/common/ast_proto.cc
index 8e097a266..5fcf21f80 100644
--- a/common/ast_proto.cc
+++ b/common/ast_proto.cc
@@ -14,7 +14,6 @@
 
 #include "common/ast_proto.h"
 
-#include <cstddef>
 #include <cstdint>
 #include <memory>
 #include <string>
@@ -57,7 +56,7 @@ using ::cel::ast_internal::FunctionType;
 using ::cel::ast_internal::ListType;
 using ::cel::ast_internal::MapType;
 using ::cel::ast_internal::MessageType;
-using ::cel::ast_internal::NullValue;
+using ::cel::ast_internal::NullType;
 using ::cel::ast_internal::ParamType;
 using ::cel::ast_internal::PrimitiveType;
 using ::cel::ast_internal::PrimitiveTypeWrapper;
@@ -234,7 +233,7 @@ absl::StatusOr<Type> ConvertProtoTypeToNative(
     case cel::expr::Type::kDyn:
       return Type(DynamicType());
     case cel::expr::Type::kNull:
-      return Type(nullptr);
+      return Type(NullType());
     case cel::expr::Type::kPrimitive: {
       auto native_primitive = ToNative(type.primitive());
       if (!native_primitive.ok()) {
@@ -395,7 +394,7 @@ struct TypeKindToProtoVisitor {
     return absl::OkStatus();
   }
 
-  absl::Status operator()(std::nullptr_t) {
+  absl::Status operator()(NullType) {
     result->set_null(google::protobuf::NULL_VALUE);
     return absl::OkStatus();
   }
diff --git a/common/ast_proto_test.cc b/common/ast_proto_test.cc
index 3d8b31af6..4837a413d 100644
--- a/common/ast_proto_test.cc
+++ b/common/ast_proto_test.cc
@@ -311,7 +311,7 @@ TEST(AstConvertersTest, NullTypeToNative) {
   auto native_type = ConvertProtoTypeToNative(type);
 
   ASSERT_TRUE(native_type->has_null());
-  EXPECT_EQ(native_type->null(), nullptr);
+  EXPECT_EQ(native_type->null(), ast_internal::NullType());
 }
 
 TEST(AstConvertersTest, PrimitiveTypeWrapperToNative) {
diff --git a/runtime/internal/convert_constant.cc b/runtime/internal/convert_constant.cc
index 6a33cfb0b..a9effd229 100644
--- a/runtime/internal/convert_constant.cc
+++ b/runtime/internal/convert_constant.cc
@@ -14,6 +14,7 @@
 
 #include "runtime/internal/convert_constant.h"
 
+#include <cstddef>
 #include <cstdint>
 
 #include "absl/status/status.h"
@@ -21,7 +22,6 @@
 #include "absl/time/time.h"
 #include "absl/types/variant.h"
 #include "common/allocator.h"
-#include "common/ast/expr.h"
 #include "common/constant.h"
 #include "common/value.h"
 #include "eval/internal/errors.h"
@@ -36,10 +36,7 @@ struct ConvertVisitor {
   absl::StatusOr<cel::Value> operator()(absl::monostate) {
     return absl::InvalidArgumentError("unspecified constant");
   }
-  absl::StatusOr<cel::Value> operator()(
-      const cel::ast_internal::NullValue& value) {
-    return NullValue();
-  }
+  absl::StatusOr<cel::Value> operator()(std::nullptr_t) { return NullValue(); }
   absl::StatusOr<cel::Value> operator()(bool value) { return BoolValue(value); }
   absl::StatusOr<cel::Value> operator()(int64_t value) {
     return IntValue(value);
diff --git a/testutil/baseline_tests_test.cc b/testutil/baseline_tests_test.cc
index 28ca73a52..cf7027982 100644
--- a/testutil/baseline_tests_test.cc
+++ b/testutil/baseline_tests_test.cc
@@ -194,7 +194,7 @@ INSTANTIATE_TEST_SUITE_P(
         TestCase{AstType(ast_internal::WellKnownType::kTimestamp),
                  "x~google.protobuf.Timestamp"},
         TestCase{AstType(ast_internal::DynamicType()), "x~dyn"},
-        TestCase{AstType(nullptr), "x~null"},
+        TestCase{AstType(ast_internal::NullType()), "x~null"},
         TestCase{AstType(ast_internal::UnspecifiedType()), "x~<error>"},
         TestCase{AstType(ast_internal::MessageType("com.example.Type")),
                  "x~com.example.Type"},