I was facing the similar problem with Spring-boot-2 applications with Java 9 library.
Adding the following dependency in my pom.xml solved the issue for me:
<dependency>
<groupId>com.googlecode.slf4j-maven-plugin-log</groupId>
<artifactId>slf4j-maven-plugin-log</artifactId>
<version>1.0.0</version>
</dependency>