No converter found capable of converting from type [java.lang.String] to type [org.springframework.expression.Expression]

[kelseyh]

Describe the issue
Upgrading from spring-cloud-stream 2023.0.3 to 2023.0.4 results in the following error:

Failed to bind properties under 'spring.cloud.stream.kafka.default.producer.message-key-expression' to org.springframework.expression.Expression:

    Property: spring.cloud.stream.kafka.default.producer.message-key-expression
    Value: "headers['id']"
    Origin: class path resource [application.yml] - 5:48
    Reason: org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [java.lang.String] to type [org.springframework.expression.Expression]

This looks like a regression bug that was previously reported in #2283

To Reproduce

1. Generate a new project from https://start.spring.io/index.html (spring-boot: 3.3.6, spring-cloud: 2023.0.4)
2. Add the kafka binder

<dependency>
  <groupId>org.springframework.cloud</groupId>
  <artifactId>spring-cloud-stream-binder-kafka</artifactId>
</dependency>

3. use the following application.yml

spring:
  application.name: demo
  cloud:
    stream:
      kafka:
        default.producer.message-key-expression: headers['id']
        binder:
          brokers: localhost:9092
      bindings:
        test-out-0:
          destination: out
        test-in-0:
          destination: in
          group: test

Add a consumer in the Application.class

	@Bean
	public Consumer<Message<String>> test() {
		return message -> System.out.println("Received message: " + message);
	}

4. run mvn spring-boot:run
5. Error will be printed out in the logs.

Version of the framework
2023.0.4
Expected behavior
Should convert the expression as it does in 2023.0.3

[olegz]

Yes indeed a regression after fixing #2974