Unable to pass custom properties to custom generator

I'm developing a custom OpenAPI Generator and would like to execute specific logic based on custom configuration properties defined in the Maven plugin configuration.

Here’s an example of my plugin configuration in the pom.xml:

<plugin>
        <groupId>org.openapitools</groupId>
        <artifactId>openapi-generator-maven-plugin</artifactId>
        <version>${openapi-maven-plugin-version}</version>
        <executions>
          <execution>
            <id>generate</id>
            <goals>
              <goal>generate</goal>
            </goals>
            <configuration combine.self="append">
              <inputSpec>${swagger.desc.dir}/${swagger.desc.filename}</inputSpec>
              <generatorName>${swagger-generator}</generatorName>
              <generateApis>${generate-apis}</generateApis>
              <additionalProperties>
                <customProperty>true</customProperty>
              </additionalProperties>
            </configuration>
          </execution>
        </executions>
      </plugin>

In my custom generator class (Java), I want to retrieve and use this property for example :
Boolean isCustom = (Boolean) additionalProperties.get("customProperty");
However, when I attempt to access it, it returns null.
Is there a way to declare and retrieve custom properties ?

Start with the Maven plugin's handling of the additionalProperties configuration and trace how those values reach the custom generator class. Reproduce the provided pom.xml configuration, verify whether customProperty is forwarded and typed as expected, and add or update a focused regression test showing that the property is available to the generator.