code: private void validate() {
      if (Strings.emptyToNull(random) == null) {
        random = Strings.emptyToNull(getProject().getProperty(SYSPROP_RANDOM_SEED())); 
      }
      
      if (random == null) {
        throw new BuildException("Required attribute 'seed' must not be empty. Look at <junit4:pickseed>.");
      }
      
      long[] seeds = SeedUtils.parseSeedChain(random);
      if (seeds.length < 1) {
        throw new BuildException("Random seed is required.");
      }
      
      if (values.isEmpty() && !allowUndefined) {
        throw new BuildException("No values to pick from and allowUndefined=false.");
      }
    }
docs: Validate arguments and state.