Error with Axis2 Maven plugin

Question

I've been trying to create a WSDL from my Java code using the plugin supplied by Axis2, see here.

However when executing the goal:

mvn axis2-java2wsdl:java2wsdl

I get the following error:

Failed to execute goal org.apache.axis2:axis2-java2wsdl-maven-plugin:1.6.3:java2wsdl (default-cli) on project enterprise-assignment: null: MojoExecutionException: NullPointerException -> [Help 1]

Can anyone shed any light on the problem? My project compiles, runs and installs correctly so I'm pretty sure it's not an error in my code, but perhaps something I'm missing in my pom.

Edit: My Pom:

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xmlns="http://maven.apache.org/POM/4.0.0"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>
    <packaging>war</packaging>
    <version>1.0-SNAPSHOT</version>

    <groupId>org.andrewvincent</groupId>
    <artifactId>enterprise-assignment</artifactId>

    <properties>
        <app.id>enterprise-programming-1109</app.id>
        <app.version>1</app.version>
        <appengine.version>1.9.28</appengine.version>
        <gcloud.plugin.version>2.0.9.81.v20151008</gcloud.plugin.version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <spring.version>4.2.2.RELEASE</spring.version>
        <cxf.version>3.1.4</cxf.version>
        <maven.compiler.showDeprecation>true</maven.compiler.showDeprecation>
        <axis2.version>1.6.3</axis2.version>
    </properties>

    <prerequisites>
        <maven>3.1.0</maven>
    </prerequisites>

    <dependencies>
        <!-- Compile/runtime dependencies -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>servlet-api</artifactId>
            <version>2.5</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>jstl</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-web</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-jdbc</artifactId>
            <version>${spring.version}</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>5.1.37</version>
        </dependency>
        <dependency>
            <groupId>org.codehaus.jackson</groupId>
            <artifactId>jackson-mapper-asl</artifactId>
            <version>1.9.13</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>2.6.3</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.6.3</version>
        </dependency>
    <build>
        <!-- for hot reload of the web application-->
        <outputDirectory>${project.build.directory}/${project.build.finalName}/WEB-INF/classes</outputDirectory>
        <plugins>
            <plugin>
                <groupId>org.apache.axis2</groupId>
                <artifactId>axis2-java2wsdl-maven-plugin</artifactId>
                <version>${axis2.version}</version>
                <configuration>
                    <className>org.andrewvincent.dao.StaffDAO</className>
                </configuration>
                <executions>
                    <execution>
                        <goals>
                            <goal>java2wsdl</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>versions-maven-plugin</artifactId>
                <version>2.2</version>
                <executions>
                    <execution>
                        <phase>compile</phase>
                        <goals>
                            <goal>display-dependency-updates</goal>
                            <goal>display-plugin-updates</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <version>3.3</version>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.7</source>
                    <target>1.7</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>2.6</version>
                <configuration>
                    <archiveClasses>true</archiveClasses>
                    <webResources>
                        <!-- in order to interpolate version from pom into appengine-web.xml -->
                        <resource>
                            <directory>${basedir}/src/main/webapp/WEB-INF</directory>
                            <filtering>true</filtering>
                            <targetPath>WEB-INF</targetPath>
                        </resource>
                    </webResources>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>