Gradle build error is unclear when no main class is specified or the main class could not be resolved #12712
Description
This is, admittedly, a very low-priority issue.
If, for some reason (I just answered a StackOverflow question about that problem), there is no main class configured, and the Spring Boot gradle plugin can't resolve any main class, the bootJar task fails with the following error:
The value of a manifest attribute must not be null (Key=Start-Class)
This error message could be clearer, and clearly state that the specified main class is null, or that no main class could be resolved.