package com.lynbrookrobotics.potassium

import squants.Time

abstract class Component[T](period: Time)(implicit val clock: Clock) {
  def defaultController: PeriodicSignal[T]
  private var currentController: PeriodicSignal[T] = defaultController

  def setController(controller: PeriodicSignal[T]): Unit = {
    currentController.detachTickSource(this)
    controller.attachTickSource(this)
    currentController = controller
  }

  def resetToDefault(): Unit = {
    setController(defaultController)
  }

  def applySignal(signal: T): Unit

  clock(period) { dt =>
    if (currentController == null) {
      currentController = defaultController
    }

    applySignal(currentController.currentValue(dt))
  }
}

package com.lynbrookrobotics.potassium

import squants.Time

abstract class Component[T](period: Time)(implicit val clock: Clock) {
  def defaultController: PeriodicSignal[T]
  private var currentController: PeriodicSignal[T] = defaultController

  def setController(controller: PeriodicSignal[T]): Unit = {
    currentController.detachTickSource(this)
    controller.attachTickSource(this)
    currentController = controller
  }

  def resetToDefault(): Unit = {
    setController(defaultController)
  }

  def applySignal(signal: T): Unit

  clock(period) { dt =>
    applySignal(currentController.currentValue(dt))
  }
}

--- 
+++ 
@@ -19,6 +19,10 @@
   def applySignal(signal: T): Unit
 
   clock(period) { dt =>
+    if (currentController == null) {
+      currentController = defaultController
+    }
+
     applySignal(currentController.currentValue(dt))
   }
 }
Add check for late default controller initialization in components
