Update Kotlin [1.7.20 -> 1.8.20], coroutines [1.7.3] and dokka [1.8.20]

Author: greenrobot-team

build.gradle.kts

@@ -38,9 +38,12 @@ buildscript {
     val essentialsVersion by extra("3.1.0")
     val junitVersion by extra("4.13.2")
     val mockitoVersion by extra("3.8.0")
-    val kotlinVersion by extra("1.7.20")
-    val coroutinesVersion by extra("1.6.4")
-    val dokkaVersion by extra("1.7.20")
+    // The versions of Kotlin, Kotlin Coroutines and Dokka must work together.
+    // Check https://github.com/Kotlin/kotlinx.coroutines#readme
+    // and https://github.com/Kotlin/dokka/releases
+    val kotlinVersion by extra("1.8.20")
+    val coroutinesVersion by extra("1.7.3")
+    val dokkaVersion by extra("1.8.20")
 
     println("version=$obxJavaVersion")
     println("objectboxNativeDependency=$obxJniLibVersion")

objectbox-rxjava3/src/main/java/io/objectbox/rx3/Query.kt

@@ -9,7 +9,7 @@ import io.reactivex.rxjava3.core.Single
 /**
  * Shortcut for [`RxQuery.flowableOneByOne(query, strategy)`][RxQuery.flowableOneByOne].
  */
-fun <T> Query<T>.flowableOneByOne(strategy: BackpressureStrategy = BackpressureStrategy.BUFFER): Flowable<T> {
+fun <T : Any> Query<T>.flowableOneByOne(strategy: BackpressureStrategy = BackpressureStrategy.BUFFER): Flowable<T> {
     return RxQuery.flowableOneByOne(this, strategy)
 }