Webflux coroutine controller responds with "COROUTINE_SUSPENDED" string

[sgornostal]

Build:

...
plugins {
	id("org.springframework.boot") version "2.1.5.RELEASE"
	id("io.spring.dependency-management") version "1.0.7.RELEASE"
	kotlin("jvm") version "1.3.31"
	kotlin("plugin.spring") version "1.3.31"
}
...
dependencies {
	implementation("org.springframework.boot:spring-boot-starter-data-mongodb-reactive")
	implementation("org.springframework.boot:spring-boot-starter-webflux")
	implementation("org.springframework.kotlin:spring-webflux-kotlin-coroutine:0.3.7")
	implementation("org.springframework.kotlin:spring-data-mongodb-kotlin-coroutine:0.3.7")
	implementation("org.springframework.kotlin:spring-boot-autoconfigure-kotlin-coroutine:0.3.7")
	implementation("com.fasterxml.jackson.module:jackson-module-kotlin")
	implementation("org.jetbrains.kotlin:kotlin-reflect")
	implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8")
	implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.3.0-M1")
	implementation("org.jetbrains.kotlinx:kotlinx-coroutines-reactor:1.3.0-M1")
}
...

Application configuration:

@Configuration
@EnableCoroutine
@EnableCoroutineMongoRepositories
class ApplicationConfiguration

Controller:

@Document(collection = "person")
data class Person(@Id val id: String? = null, val name: String)

interface PersonRepository : CoroutineMongoRepository<Person, String>

data class PersonForm(val name: String)

@RestController
@RequestMapping("/persons")
class PersonController(private val personRepository: PersonRepository) {

    @GetMapping
    suspend fun find(): List<Person> = personRepository.findAll()

    @PostMapping
    suspend fun create(@RequestBody form: PersonForm): Person = personRepository.save(Person(name = form.name))

}

When I send either GET or POST request, server responds with "COROUTINE_SUSPENDED":

GET http://localhost:8080/persons

HTTP/1.1 200 OK
Content-Type: application/json;charset=UTF-8
Content-Length: 21
Cache-Control: no-cache, no-store, max-age=0, must-revalidate
Pragma: no-cache
Expires: 0
X-Content-Type-Options: nosniff
X-Frame-Options: DENY
X-XSS-Protection: 1 ; mode=block
Referrer-Policy: no-referrer

"COROUTINE_SUSPENDED"

Response code: 200 (OK); Time: 9ms; Content length: 21 bytes

It looks like a problem with webflux coroutine because data are stored to database.