JIRA: https://jira.spring.io/browse/INT-4222
See INT-4214; the `DefaultMessageHandlerMethodFactory` requires a conversion service
and sets up a default.
Some SI components propagated a `null` conversion service which overwrote the default
causing runtime exceptions.
Caused by: java.lang.IllegalArgumentException: ConversionService must not be null
at org.springframework.util.Assert.notNull(Assert.java:163) ~[spring-core-5.0.0.BUILD-SNAPSHOT.jar:5.0.0.BUILD-SNAPSHOT]