diff --git a/controls-core/src/commonMain/kotlin/space/kscience/controls/spec/DeviceBase.kt b/controls-core/src/commonMain/kotlin/space/kscience/controls/spec/DeviceBase.kt
index 0f5436b..034485f 100644
--- a/controls-core/src/commonMain/kotlin/space/kscience/controls/spec/DeviceBase.kt
+++ b/controls-core/src/commonMain/kotlin/space/kscience/controls/spec/DeviceBase.kt
@@ -25,9 +25,9 @@ private suspend fun <D : Device, T> DevicePropertySpec<D, T>.readMeta(device: D)
 
 private suspend fun <D : Device, I, O> DeviceActionSpec<D, I, O>.executeWithMeta(
     device: D,
-    item: Meta?,
+    item: Meta,
 ): Meta? {
-    val arg = item?.let { inputConverter.metaToObject(item) }
+    val arg: I = inputConverter.metaToObject(item) ?: error("Failed to convert $item with $inputConverter")
     val res = execute(device, arg)
     return res?.let { outputConverter.objectToMeta(res) }
 }
@@ -146,7 +146,7 @@ public abstract class DeviceBase<D : Device>(
 
     override suspend fun execute(actionName: String, argument: Meta?): Meta? {
         val spec = actions[actionName] ?: error("Action with name $actionName not found")
-        return spec.executeWithMeta(self, argument)
+        return spec.executeWithMeta(self, argument ?: Meta.EMPTY)
     }
 
 }
diff --git a/controls-core/src/commonMain/kotlin/space/kscience/controls/spec/DevicePropertySpec.kt b/controls-core/src/commonMain/kotlin/space/kscience/controls/spec/DevicePropertySpec.kt
index 0e72fca..ce83edc 100644
--- a/controls-core/src/commonMain/kotlin/space/kscience/controls/spec/DevicePropertySpec.kt
+++ b/controls-core/src/commonMain/kotlin/space/kscience/controls/spec/DevicePropertySpec.kt
@@ -66,7 +66,7 @@ public interface DeviceActionSpec<in D : Device, I, O> {
     /**
      * Execute action on a device
      */
-    public suspend fun execute(device: D, input: I?): O?
+    public suspend fun execute(device: D, input: I): O
 }
 
 /**
@@ -137,5 +137,8 @@ public suspend fun <D : Device> D.invalidate(propertySpec: DevicePropertySpec<D,
 /**
  * Execute the action with name according to [actionSpec]
  */
-public suspend fun <I, O, D : Device> D.execute(actionSpec: DeviceActionSpec<D, I, O>, input: I? = null): O? =
-    actionSpec.execute(this, input)
\ No newline at end of file
+public suspend fun <I, O, D : Device> D.execute(actionSpec: DeviceActionSpec<D, I, O>, input: I): O =
+    actionSpec.execute(this, input)
+
+public suspend fun <O, D : Device> D.execute(actionSpec: DeviceActionSpec<D, Unit, O>): O =
+    actionSpec.execute(this, Unit)
\ No newline at end of file
diff --git a/controls-core/src/commonMain/kotlin/space/kscience/controls/spec/DeviceSpec.kt b/controls-core/src/commonMain/kotlin/space/kscience/controls/spec/DeviceSpec.kt
index eb5c978..ff7dddd 100644
--- a/controls-core/src/commonMain/kotlin/space/kscience/controls/spec/DeviceSpec.kt
+++ b/controls-core/src/commonMain/kotlin/space/kscience/controls/spec/DeviceSpec.kt
@@ -12,6 +12,13 @@ import kotlin.reflect.KMutableProperty1
 import kotlin.reflect.KProperty
 import kotlin.reflect.KProperty1
 
+public object UnitMetaConverter: MetaConverter<Unit>{
+    override fun metaToObject(meta: Meta): Unit = Unit
+
+    override fun objectToMeta(obj: Unit): Meta = Meta.EMPTY
+}
+
+public val MetaConverter.Companion.unit: MetaConverter<Unit> get() = UnitMetaConverter
 
 @OptIn(InternalDeviceAPI::class)
 public abstract class DeviceSpec<D : Device> {
@@ -165,7 +172,7 @@ public abstract class DeviceSpec<D : Device> {
         outputConverter: MetaConverter<O>,
         descriptorBuilder: ActionDescriptor.() -> Unit = {},
         name: String? = null,
-        execute: suspend D.(I?) -> O?,
+        execute: suspend D.(I) -> O,
     ): PropertyDelegateProvider<DeviceSpec<D>, ReadOnlyProperty<DeviceSpec<D>, DeviceActionSpec<D, I, O>>> =
         PropertyDelegateProvider { _: DeviceSpec<D>, property ->
             val actionName = name ?: property.name
@@ -175,7 +182,7 @@ public abstract class DeviceSpec<D : Device> {
                 override val inputConverter: MetaConverter<I> = inputConverter
                 override val outputConverter: MetaConverter<O> = outputConverter
 
-                override suspend fun execute(device: D, input: I?): O? = withContext(device.coroutineContext) {
+                override suspend fun execute(device: D, input: I): O = withContext(device.coroutineContext) {
                     device.execute(input)
                 }
             }
@@ -191,7 +198,7 @@ public abstract class DeviceSpec<D : Device> {
     public fun metaAction(
         descriptorBuilder: ActionDescriptor.() -> Unit = {},
         name: String? = null,
-        execute: suspend D.(Meta?) -> Meta?,
+        execute: suspend D.(Meta) -> Meta,
     ): PropertyDelegateProvider<DeviceSpec<D>, ReadOnlyProperty<DeviceSpec<D>, DeviceActionSpec<D, Meta, Meta>>> =
         action(
             MetaConverter.Companion.meta,
@@ -209,15 +216,14 @@ public abstract class DeviceSpec<D : Device> {
         descriptorBuilder: ActionDescriptor.() -> Unit = {},
         name: String? = null,
         execute: suspend D.() -> Unit,
-    ): PropertyDelegateProvider<DeviceSpec<D>, ReadOnlyProperty<DeviceSpec<D>, DeviceActionSpec<D, Meta, Meta>>> =
+    ): PropertyDelegateProvider<DeviceSpec<D>, ReadOnlyProperty<DeviceSpec<D>, DeviceActionSpec<D, Unit, Unit>>> =
         action(
-            MetaConverter.Companion.meta,
-            MetaConverter.Companion.meta,
+            MetaConverter.Companion.unit,
+            MetaConverter.Companion.unit,
             descriptorBuilder,
             name
         ) {
             execute()
-            null
         }
 }
 
diff --git a/demo/all-things/src/main/kotlin/space/kscience/controls/demo/DemoDevice.kt b/demo/all-things/src/main/kotlin/space/kscience/controls/demo/DemoDevice.kt
index 37b7b4b..dd65b78 100644
--- a/demo/all-things/src/main/kotlin/space/kscience/controls/demo/DemoDevice.kt
+++ b/demo/all-things/src/main/kotlin/space/kscience/controls/demo/DemoDevice.kt
@@ -68,11 +68,10 @@ class DemoDevice(context: Context, meta: Meta) : DeviceBySpec<IDemoDevice>(Compa
         }
 
 
-        val resetScale by action(MetaConverter.meta, MetaConverter.meta) {
+        val resetScale by unitAction {
             write(timeScale, 5000.0)
             write(sinScale, 1.0)
             write(cosScale, 1.0)
-            null
         }
 
         override suspend fun IDemoDevice.onOpen() {