Invalid Groovy compiler level: null when running eclipse plugin

[marioja]

I get the following errors whenever I run my custom eclipse headless plugin (that implements the org.eclipse.core.runtime.applications extension) inside an eclipse that includes the groovy eclipse plugin.

Invalid Groovy compiler level: null
Must be one of 16, 1.6, 17, 1.7, 18, 1.8, 19, 1.9, 20, 2.0, 21, 2.1, 22, 2.2, 23, 2.3, 24, 2.4, 25, 2.5, 26, 2.6, 30 or 3.0
Invalid Groovy compiler level: null
org.eclipse.m2e.logback.configuration: SLF4J logger factory is not an instance of LoggerContext: org.slf4j.impl.Log4jLoggerFactory
Must be one of 16, 1.6, 17, 1.7, 18, 1.8, 19, 1.9, 20, 2.0, 21, 2.1, 22, 2.2, 23, 2.3, 24, 2.4, 25, 2.5, 26, 2.6, 30 or 3.0
Invalid Groovy compiler level: null
Must be one of 16, 1.6, 17, 1.7, 18, 1.8, 19, 1.9, 20, 2.0, 21, 2.1, 22, 2.2, 23, 2.3, 24, 2.4, 25, 2.5, 26, 2.6, 30 or 3.0
Starting Groovy-Eclipse compiler resolver. Specified compiler level: unspecified
2333 org.codehaus.groovy_2.5.8.v202001062233-e1912 STARTING
3529 org.codehaus.groovy_2.4.17.v202001062233-e1912 STARTING
Skipped bundle version 2.5.8.v202001062233-e1912
Stopped bundle version 2.4.17.v202001062233-e1912
Refresh bundles:
3529 org.codehaus.groovy_2.4.17.v202001062233-e1912 UNINSTALLED

I know that when I run Eclipse GUI, the eclipse preferences sets the default compiler level but I would like to know what I need to do whenever I run my custom headless plugin to set the default compiler level and avoid getting this error whenever I run my eclipse plugin. Any help is much appreciated. My custom plugin seems to work fine because it does not use groovy.

[marioja]

Upon looking at the source code it looks like the -Dgroovy.compiler.level=25 for example would eliminate the errors. This is an acceptable work-around but in reality, the eclipse groovy compiler preferences should kick in and be recognized whether eclipse is running a gui or headless. This should be fixed.