IntelliJ IDEA says that <systemProperties/> element is not allowed inside <configuration/> - maven

Question

I'm using a plugin in maven that uses Jetty.
In this plugin, I need to made a configuration to set maxFormContentSize:
<plugin>
<groupId>com.organization.example</groupId>
<artifactId>maven-example-plugin</artifactId>
<version>${example.version}</version>
<dependencies>
<!-- -->
</dependencies>
<configuration>
<systemProperties>
<systemProperty>
<name>org.mortbay.jetty.Request.maxFormContentSize</name>
<value>500000</value>
</systemProperty>
</systemProperties>
<script>${example.script}</script>
</configuration>
</plugin>
The problem is that Intellij IDEA says that systemProperties element is not allowed here:
Element systemProperties is not allowed here
What is the correct configuration for the IntelliJ IDEA not show this error? I already made a research about this subject but appears that is the only possible configuration.
I'm using maven 2.2.1 and IntelliJ IDEA 2017.1.4. The Jetty version is 7.6.8.v20121106.

Answer 1

The <configuration> section of a maven plugin can only contain what that specific plugin supports in its various goals.
Not all maven plugins support <systemProperties> only certain ones do.
Since you stubbed out the actual plugin you are struggling with I cannot link you to the specific plugin's documentation page for its goals and configurations.
Look for something like this ...
http://maven.apache.org/plugins/maven-javadoc-plugin/javadoc-mojo.html
... but for your specific plugin
Ask Maven
You can also ask maven, on its command line, to describe the plugin and even a specific goal in the plugin.
Note: the below example command lines work with maven-help-plugin v2.2 or better.
Describe all of the goals:
$ mvn help:describe -DgroupId=org.eclipse.jetty \
-DartifactId=jetty-maven-plugin \
-Dversion=9.4.6.v20170531
Describe a specific goal in detail (with parameters):
$ mvn help:describe -DgroupId=org.eclipse.jetty \
-DartifactId=jetty-maven-plugin \
-Dversion=9.4.6.v20170531 \
-Dgoal=start \
-Ddetail=true