Leverage Kotlin null-safety

Utilize Kotlin’s null-safety features effectively to create cleaner, more robust code:

1. For class properties that will be initialized before use, prefer lateinit var over nullable types with ?: ```kotlin // Avoid private var server: MockWebServer? = null

// Prefer private lateinit var server: MockWebServer

2. Design API signatures to minimize forcing clients to use the unsafe `!!` operator:
```kotlin
// Avoid
suspend fun <T : Any> TransactionalOperator.executeAndAwait(f: suspend (ReactiveTransaction) -> T?): T?

// Prefer
suspend fun <T> TransactionalOperator.executeAndAwait(f: suspend (ReactiveTransaction) -> T): T

1. Avoid redundant null checks when Kotlin’s null-safety operators are already in use: ```kotlin // Redundant val ctor = BeanUtils.findPrimaryConstructor(SomeClass::class.java)!! assertThat(ctor).isNotNull() // Unnecessary since !! already asserts non-null

// Cleaner val ctor = BeanUtils.findPrimaryConstructor(SomeClass::class.java)!! // Continue using ctor directly ```