Enable strict JSR-305 mode

build.gradle.kts

@@ -58,7 +58,10 @@ allprojects {
     }
 
     tasks.withType<KotlinCompile> {
-        kotlinOptions.jvmTarget = "1.8"
+        kotlinOptions {
+            jvmTarget = "1.8"
+            freeCompilerArgs = listOf("-Xjsr305=strict")
+        }
     }
 
     tasks.withType<AbstractArchiveTask> {