diff --git a/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/command/descriptor/CommandDescriptor.kt b/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/command/descriptor/CommandDescriptor.kt
index 1e0a9af2a..690694d4e 100644
--- a/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/command/descriptor/CommandDescriptor.kt
+++ b/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/command/descriptor/CommandDescriptor.kt
@@ -31,16 +31,18 @@ public interface CommandSignatureVariant {
 @ExperimentalCommandDescriptors
 public interface ICommandParameter<T : Any?> {
     public val name: String
-    public val type: KType
+
+    /**
+     * If [isOptional] is `false`, [defaultValue] is always `null`.
+     * Otherwise [defaultValue] may be `null` iff [T] is nullable.
+     */
     public val defaultValue: T?
+    public val isOptional: Boolean
 
-    public companion object {
-        @get:JvmStatic
-        @ExperimentalCommandDescriptors
-        public val ICommandParameter<*>.isOptional: Boolean
-            get() = this.defaultValue != null
-
-    }
+    /**
+     * Reified type of [T]
+     */
+    public val type: KType
 }
 
 @ExperimentalCommandDescriptors
@@ -54,9 +56,10 @@ public sealed class CommandValueParameter<T> : ICommandParameter<T> {
 
     public class StringConstant(
         public override val name: String,
-        public override val defaultValue: String,
     ) : CommandValueParameter<String>() {
-        override val type: KType get() = STRING_TYPE
+        public override val type: KType get() = STRING_TYPE
+        public override val defaultValue: Nothing? get() = null
+        public override val isOptional: Boolean get() = false
 
         private companion object {
             @OptIn(ExperimentalStdlibApi::class)
@@ -64,6 +67,27 @@ public sealed class CommandValueParameter<T> : ICommandParameter<T> {
         }
     }
 
+    public class UserDefinedType<T>(
+        public override val name: String,
+        public override val defaultValue: T?,
+        public override val isOptional: Boolean,
+        public override val type: KType,
+    ) : CommandValueParameter<T>() {
+        public companion object {
+            @JvmStatic
+            public inline fun <reified T : Any> createOptional(name: String, defaultValue: T): UserDefinedType<T> {
+                @OptIn(ExperimentalStdlibApi::class)
+                return UserDefinedType(name, defaultValue, true, typeOf<T>())
+            }
+
+            @JvmStatic
+            public inline fun <reified T : Any> createRequired(name: String): UserDefinedType<T> {
+                @OptIn(ExperimentalStdlibApi::class)
+                return UserDefinedType(name, null, false, typeOf<T>())
+            }
+        }
+    }
+
     /**
      * Extended by [CommandValueArgumentParser]
      */
diff --git a/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/command/parse/CommandCall.kt b/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/command/parse/CommandCall.kt
index ef04564b1..4bb43bb9e 100644
--- a/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/command/parse/CommandCall.kt
+++ b/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/command/parse/CommandCall.kt
@@ -14,8 +14,6 @@ package net.mamoe.mirai.console.command.parse
 import net.mamoe.mirai.console.command.Command
 import net.mamoe.mirai.console.command.CommandSender
 import net.mamoe.mirai.console.command.descriptor.ExperimentalCommandDescriptors
-import net.mamoe.mirai.console.command.resolve.CommandCallResolver
-import net.mamoe.mirai.console.util.ConsoleExperimentalApi
 
 /**
  * Unresolved [CommandCall].
@@ -33,10 +31,11 @@ public interface CommandCall {
      * Explicit value arguments
      */
     public val valueArguments: List<CommandValueArgument>
+}
 
-    /**
-     * Custom data for [CommandCallResolver]
-     */
-    @ConsoleExperimentalApi
-    public val customData: Map<Any, Any>
-}
\ No newline at end of file
+@ExperimentalCommandDescriptors
+public class CommandCallImpl(
+    override val caller: CommandSender,
+    override val calleeName: String,
+    override val valueArguments: List<CommandValueArgument>,
+) : CommandCall
\ No newline at end of file
diff --git a/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/extensions/CommandCallParserProvider.kt b/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/extensions/CommandCallParserProvider.kt
index d72aaa27c..a3870a932 100644
--- a/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/extensions/CommandCallParserProvider.kt
+++ b/backend/mirai-console/src/main/kotlin/net/mamoe/mirai/console/extensions/CommandCallParserProvider.kt
@@ -15,7 +15,7 @@ import net.mamoe.mirai.console.extension.AbstractExtensionPoint
 import net.mamoe.mirai.console.extension.InstanceExtension
 
 /**
- * The resolver for a [CommandCall]
+ * The provider of [CommandCallParser]
  */
 @ExperimentalCommandDescriptors
 public interface CommandCallParserProvider : InstanceExtension<CommandCallParser> {