diff --git a/RELEASE.md b/RELEASE.md
new file mode 100644
index 0000000..9792e94
--- /dev/null
+++ b/RELEASE.md
@@ -0,0 +1,3 @@
+RELEASE_TYPE: patch
+
+Internal refactor.
\ No newline at end of file
diff --git a/include/hegel/generators/combinators.h b/include/hegel/generators/combinators.h
index f1f34bc..2fb97ab 100644
--- a/include/hegel/generators/combinators.h
+++ b/include/hegel/generators/combinators.h
@@ -300,7 +300,8 @@ namespace hegel::generators {
 
             hegel::internal::json::json generators =
                 hegel::internal::json::json::array();
-            generators.push_back(hegel::internal::json::json{{"type", "null"}});
+            generators.push_back(hegel::internal::json::json{
+                {"type", "constant"}, {"value", nullptr}});
             generators.push_back(basic->schema);
             hegel::internal::json::json schema = {{"type", "one_of"},
                                                   {"generators", generators}};
diff --git a/nix/flake.lock b/nix/flake.lock
index 16cb45c..ddfc6df 100644
--- a/nix/flake.lock
+++ b/nix/flake.lock
@@ -38,17 +38,17 @@
       },
       "locked": {
         "dir": "nix",
-        "lastModified": 1777479227,
-        "narHash": "sha256-s1JjMvJX3SRebwlSQeo6S99OWIoP0CFuPALvG1itzGw=",
-        "ref": "refs/tags/v0.5.0",
-        "rev": "a95da271bb026037d13656b4317a445a308fded3",
-        "revCount": 653,
+        "lastModified": 1777568232,
+        "narHash": "sha256-VInDnyh7uxm6d9IyfV3ShxHZD4BvsTF7wIB+kv9apbk=",
+        "ref": "refs/tags/v0.6.0",
+        "rev": "4630a7845bff88908be4505675a945711f43b5bd",
+        "revCount": 658,
         "type": "git",
         "url": "https://github.com/hegeldev/hegel-core"
       },
       "original": {
         "dir": "nix",
-        "ref": "refs/tags/v0.5.0",
+        "ref": "refs/tags/v0.6.0",
         "type": "git",
         "url": "https://github.com/hegeldev/hegel-core"
       }
diff --git a/nix/flake.nix b/nix/flake.nix
index 85e166d..503c4ad 100644
--- a/nix/flake.nix
+++ b/nix/flake.nix
@@ -4,7 +4,7 @@
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
     flake-compat.url = "https://flakehub.com/f/edolstra/flake-compat/1.tar.gz";
-    hegel.url = "git+https://github.com/hegeldev/hegel-core?dir=nix&ref=refs/tags/v0.5.0";
+    hegel.url = "git+https://github.com/hegeldev/hegel-core?dir=nix&ref=refs/tags/v0.6.0";
   };
 
   outputs =
diff --git a/src/connection.cpp b/src/connection.cpp
index d1c0d40..2066910 100644
--- a/src/connection.cpp
+++ b/src/connection.cpp
@@ -18,8 +18,8 @@
 using hegel::internal::json::ImplUtil;
 
 namespace hegel::impl {
-    static constexpr const char* MIN_PROTOCOL_VERSION = "0.11";
-    static constexpr const char* MAX_PROTOCOL_VERSION = "0.11";
+    static constexpr const char* MIN_PROTOCOL_VERSION = "0.12";
+    static constexpr const char* MAX_PROTOCOL_VERSION = "0.12";
     static constexpr const char* HANDSHAKE_STRING = "hegel_handshake_start";
 
     Connection::Connection(int read_fd, int write_fd)
diff --git a/src/generators.cpp b/src/generators.cpp
index 92e6196..303c3b9 100644
--- a/src/generators.cpp
+++ b/src/generators.cpp
@@ -227,7 +227,7 @@ namespace hegel::generators {
             std::optional<BasicGenerator<std::string>>
             as_basic() const override {
                 return BasicGenerator<std::string>{
-                    {{"type", version_ == 4 ? "ipv4" : "ipv6"}},
+                    {{"type", "ip_address"}, {"version", version_}},
                     &default_parse_raw<std::string>};
             }
 
diff --git a/src/installer.h b/src/installer.h
index a58f430..1c84f11 100644
--- a/src/installer.h
+++ b/src/installer.h
@@ -12,7 +12,7 @@ namespace hegel::impl {
 
     /// hegel-core version that this library is built against. Kept in sync
     /// with the Rust library's `HEGEL_SERVER_VERSION`.
-    constexpr const char* HEGEL_SERVER_VERSION = "0.5.0";
+    constexpr const char* HEGEL_SERVER_VERSION = "0.6.0";
 
     /// Returns the argv prefix used to invoke the hegel server.
     ///