fixup! feat!: implement proper serialization logic

lib/src/core/definitions/form.dart

@@ -128,4 +128,8 @@ class Form {
 
   /// Additional fields collected during the parsing of a JSON object.
   final Map<String, dynamic> additionalFields = {};
+
+  Map<String, dynamic> toJson() {
+    throw UnimplementedError();
+  }
 }

lib/src/core/definitions/interaction_affordances/interaction_affordance.dart

@@ -55,4 +55,8 @@ sealed class InteractionAffordance {
 
   /// Additional fields that could not be deserialized as class members.
   final Map<String, dynamic>? additionalFields;
+
+  Map<String, dynamic> toJson() {
+    throw UnimplementedError();
+  }
 }

lib/src/core/definitions/thing_description.dart

@@ -168,6 +168,54 @@ class ThingDescription {
       result["description"] = description;
     }
 
+    final version = this.version;
+    if (version != null) {
+      result["version"] = version.toJson();
+    }
+
+    if (created != null) {
+      result["created"] = created.toString();
+    }
+
+    if (modified != null) {
+      result["modified"] = modified.toString();
+    }
+
+    if (support != null) {
+      result["support"] = support.toString();
+    }
+
+    if (base != null) {
+      result["base"] = base.toString();
+    }
+
+    if (id != null) {
+      result["id"] = id;
+    }
+
+    final forms = this.forms;
+    if (forms != null) {
+      result["forms"] = forms.map((form) => form.toJson());
+    }
+
+    final properties = this.properties;
+    if (properties != null) {
+      result["properties"] =
+          properties.map((key, property) => MapEntry(key, property.toJson()));
+    }
+
+    final actions = this.actions;
+    if (actions != null) {
+      result["actions"] =
+          actions.map((key, action) => MapEntry(key, action.toJson()));
+    }
+
+    final events = this.events;
+    if (events != null) {
+      result["events"] =
+          events.map((key, event) => MapEntry(key, event.toJson()));
+    }
+
     return result;
   }
 

lib/src/core/definitions/version_info.dart

@@ -48,4 +48,9 @@ class VersionInfo {
 
   /// Additional fields collected during the parsing of a JSON object.
   final Map<String, dynamic>? additionalFields;
+
+  /// Converts this [VersionInfo] to a [Map] resembling a JSON object.
+  Map<String, dynamic> toJson() {
+    throw UnimplementedError();
+  }
 }