Enable OptionalUnit rule

app/k9mail/src/release/java/app/k9mail/dev/ReleaseConfig.kt

@@ -6,4 +6,6 @@ import org.koin.core.scope.Scope
 
 fun Scope.developmentBackends() = emptyMap<String, BackendFactory>()
 
-fun Module.developmentModuleAdditions() = Unit
+fun Module.developmentModuleAdditions() {
+    // No-op
+}

app/storage/src/test/java/com/fsck/k9/preferences/StorageEditorTest.kt

@@ -181,8 +181,7 @@ class StorageEditorTest : K9RobolectricTest() {
             on { remove(any()) } doAnswer {
                 val key = it.getArgument<String>(0)
                 workingMap.remove(key)
-
-                Unit
+                return@doAnswer
             }
         }
 

app/storage/src/test/java/com/fsck/k9/storage/messages/ChunkedDatabaseOperationsTest.kt

@@ -45,7 +45,6 @@ class ChunkedDatabaseOperationsTest {
             argumentTransformation = Int::toString,
         ) { selectionSet, selectionArguments ->
             chunks.add(selectionSet to selectionArguments)
-            Unit
         }
 
         assertThat(chunks).hasSize(1)
@@ -65,7 +64,6 @@ class ChunkedDatabaseOperationsTest {
             chunkSize = 1,
         ) { selectionSet, selectionArguments ->
             chunks.add(selectionSet to selectionArguments)
-            Unit
         }
 
         assertThat(chunks).hasSize(2)
@@ -89,7 +87,6 @@ class ChunkedDatabaseOperationsTest {
             chunkSize = 5,
         ) { selectionSet, selectionArguments ->
             chunks.add(selectionSet to selectionArguments)
-            Unit
         }
 
         assertThat(chunks).hasSize(3)

cli/autodiscovery-cli/src/main/kotlin/app/k9mail/cli/autodiscovery/SerialRunner.kt

@@ -27,9 +27,7 @@ class SerialRunner(private val runnables: List<AutoDiscoveryRunnable>) {
                         networkError = discoveryResult
                     }
                 }
-                NoUsableSettingsFound -> {
-                    Unit
-                }
+                NoUsableSettingsFound -> { }
                 is UnexpectedException -> {
                     Timber.w(discoveryResult.exception, "Unexpected exception")
                 }

config/detekt/detekt.yml

@@ -663,7 +663,7 @@ style:
   OptionalAbstractKeyword:
     active: true
   OptionalUnit:
-    active: false
+    active: true
   OptionalWhenBraces:
     active: false
   PreferToOverPairSyntax:

core/ui/compose/testing/src/main/kotlin/app/k9mail/core/ui/compose/testing/ComposeTest.kt

@@ -26,7 +26,7 @@ open class ComposeTest {
 
     fun getString(@StringRes resourceId: Int): String = RuntimeEnvironment.getApplication().getString(resourceId)
 
-    fun runComposeTest(testContent: ComposeContentTestRule.() -> Unit): Unit = with(composeTestRule) {
+    fun runComposeTest(testContent: ComposeContentTestRule.() -> Unit) = with(composeTestRule) {
         testContent()
     }
 }