use maven-assembly-plugin , but jar only contain dependency project's classes, no app project classes - maven

Question

I have a library project which I declared as a <dependency> of my App project.
The library project's pom.xml:
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.my.library</groupId>
<artifactId>MyLib</artifactId>
<version>1.0</version>
<packaging>jar</packaging>
<name>MyLib</name>
...
My App project's pom.xml:
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>com.my.app</groupId>
<artifactId>MyApp</artifactId>
<version>1.0</version>
<packaging>jar</packaging>
<name>MyApp</name>
<dependencies>
<!--include library project as a dependency-->
<dependency>
<groupId>com.my.library</groupId>
<artifactId>MyLib</artifactId>
<version>1.0</version>
</dependency>
...
</dependencies>
Since I need an jar which includes classes of my library project, so I declared also maven-assembly-plugin in my App project's pom.xml:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.4</version>
<configuration>
<descriptor>assembly.xml</descriptor>
</configuration>
<executions>
<execution>
<id>make-jar</id>
<phase>package</phase>
<goals>
<goal>assembly</goal>
</goals>
</execution>
</executions>
</plugin>
The assembly.xml looks like this:
<assembly
xmlns="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.0"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.0 http://maven.apache.org/xsd/assembly-1.1.0.xsd">
<id>jar-with-dependencies</id>
<formats>
<format>jar</format>
</formats>
<includeBaseDirectory>false</includeBaseDirectory>
<dependencySets>
<dependencySet>
<outputDirectory>/</outputDirectory>
<useProjectArtifact>true</useProjectArtifact>
<unpack>true</unpack>
<scope>runtime</scope>
<includes>
<!--inclucde classes from my library project-->
<include>com.my.library:MyLib</include>
</includes>
</dependencySet>
</dependencySets>
</assembly>
Ok, at this point, I run mvn clean install under my App project, under target/ directory, I got MyApp-jar-with-dependencies.jar.
But when I check the content of above jar, it only contains classes of my library project but doesn't contain my App project's classes? WHY?