According to the documentation, the possible return values of the step compareVersions are -1, 0 and 1.

The following code snippet gives a return value of -2.

// Scripted syntax
node {
    stage('test') {
        String tag1 = '1.2.3'
        String tag2 = '1.2.3-myBranch-SNAPSHOT'
        def comparisonResult = compareVersions(v1: tag1, v2: tag2)
        echo comparisonResult.toString()
    }
} 

Inverting arguments v1 and v2 results in -2 as the return value.

This return value is not documented.

• Is this a bug?
• Is the documentation incomplete?

If the latter, what is the logic behind this return value, and how does it differ from -1 (or 1)?