Exception starting karaf custom distro "minimal example" from docs

[tom]

I've attempted to build a simple custom Karaf distribution using the maven 
plugin and the karaf-assembly packaging.
I can build the assembly, but when I start the result I get an exception.

My pom configuration is currently very simple, just:

   <dependencies>
        <dependency>
            <groupId>org.apache.karaf.features</groupId>
            <artifactId>framework</artifactId>
            <version>${karafVersion}</version>
            <type>kar</type>
        </dependency>
        <dependency>
            <groupId>org.apache.karaf.features</groupId>
            <artifactId>standard</artifactId>
            <version>${karafVersion}</version>
            <classifier>features</classifier>
            <type>xml</type>
                        <scope>compile</scope>
        </dependency>

   ...

            <plugin>
                <groupId>org.apache.karaf.tooling</groupId>
                <artifactId>karaf-maven-plugin</artifactId>
                <configuration>
                    <!-- <startupFeatures/> -->
                    <bootFeatures>
                        <!-- standard distribution -->
                        <feature>standard</feature>
                        <!-- minimal distribution -->
                        <!--<feature>minimal</feature>-->
                    </bootFeatures>
                    <javase>1.8</javase>
                </configuration>
            </plugin>


karafVersion is 4.1.1

So I'm just bundling karaf, I'm not including anything else. This is the 
"minimal example" in the karaf docs.

On startup I get the log here : 
https://gist.github.com/tomq42/47403ec44413fdc517c70dc3cccbf0cb

I get the same if I specify "minimal" in "bootFeatures". 
Am I doing something wrong here? 

Thanks.