I want to have a nullable bean in my koin application, like:
single(named("NULLABLE")) {
System.getenv("NULLABLE")
}
I.e. if the environment variable "NULLABLE" is set, then a bean (a string here) named "NULLABLE" will have its value, otherwise it will be null.
The usage could be like:
init {
startKoin {
modules(listOf(module))
}
}
val nullableString: String? by inject(named("NULLABLE"))
However, if there is no environment variable named "NULLABLE" I get the exception:
Exception in thread "main" java.lang.IllegalStateException: Single instance created couldn't return value
at org.koin.core.instance.SingleDefinitionInstance.get(SingleDefinitionInstance.kt:42)
at org.koin.core.definition.BeanDefinition.resolveInstance(BeanDefinition.kt:70)
at org.koin.core.scope.Scope.resolveInstance(Scope.kt:165)
at org.koin.core.scope.Scope.get(Scope.kt:128)
It's because currently a SingleDefinitionInstance throws an exception when the factory lambda returned null:
override fun <T> get(context: InstanceContext): T {
if (value == null) {
value = create(context)
}
return value as? T ?: error("Single instance created couldn't return value")
}
Is it possible to have a nullable (optional) beans in Koin?