JavaCompile.options.DebugOptions default to 'null' even when 'options.debug' is set to 'true'?

I’ve got my JavaCompile tasks defined as below:

subprojects {
tasks.withType(JavaCompile).all {
        it.options.encoding = 'iso-8859-1'
        it.sourceCompatibility '1.5'
        it.targetCompatibility '1.5'
        it.options.fork(memoryInitialSize: "1G", memoryMaximumSize: "1G")
        it.options.debug = true
        it.options.deprecation = false
        it.options.incremental = true
          it.doLast {
            println "################ " + options.debugOptions.debugLevel
        }
    }
}

The ‘debugLevel’ gets printed out is always ‘null’.

However, by looking at the generated class file, I can see that it include all the debugging information ,i.e. source, lines and vars. This was fine until I checked out the documentation of ‘DebugOptions.getDebugLevel()’ method. It says the following at the end:

By default, **only source and line** debugging information will be generated.

Assume the above statement is correct, then ‘options.debugOptions’ should not be null when ‘options.debug=true’ and should be set to ‘source,lines’. Otherwise, the documentation of ‘getDebugLevel()’ method should be updated to reflect the acutal behaviour.

Or am I miss understanding something here?