[rules-users] Planner has trouble creating a configurer: how to debug

[aitchnyu]

I tried to create a solver from XML configuration. But the entire process
returns a *cryptic error message *that makes no sense.

How do I fix this? And how can I make sense of this to actually solve
similar problems like this? 

Please excuse me if I made any bad karma. This is my first post on this (and
any) mailing list.

    jesvin at Jesvin-Technovia:~/dev/drools/sudoku$ java App 
    Exception in thread "main" java.lang.NullPointerException
    	at
org.drools.planner.core.domain.solution.SolutionDescriptor.processPropertyAnnotations(SolutionDescriptor.java:69)
    	at
org.drools.planner.core.domain.solution.SolutionDescriptor.<init>(SolutionDescriptor.java:61)
    	at
org.drools.planner.config.solver.SolverConfig.buildSolutionDescriptor(SolverConfig.java:197)
    	at
org.drools.planner.config.solver.SolverConfig.buildSolver(SolverConfig.java:167)
    	at
org.drools.planner.config.XmlSolverConfigurer.buildSolver(XmlSolverConfigurer.java:103)
    	at App.createSolver(App.java:62)
    	at App.main(App.java:40)

The function that throws it is listed here. The line is of course `return
configurer.buildSolver();`.

    private static Solver createSolver(){
	XmlSolverConfigurer configurer = new XmlSolverConfigurer();
	File file = new File("solver.xml");
	FileInputStream fin = null;
	try{
	    fin = new FileInputStream(file);	
	}
	catch(IOException e){
	     System.out.println("Unable to read drl");
	}
	configurer.configure(fin);
        //configurer.configure("/home/jesvin/dev/drools/sudoku/solver.xml");
        return configurer.buildSolver();
    }

The content of the XML:

    <?xml version="1.0" encoding="UTF-8"?>
    <solver>
      <environmentMode>DEBUG</environmentMode>
    
      <solutionClass>domain.Sudoku</solutionClass>
      <planningEntityClass>domain.Digit</planningEntityClass>
      <scoreDrl>score.drl</scoreDrl>
      <scoreDefinition>
        <scoreDefinitionType>SIMPLE</scoreDefinitionType>
      </scoreDefinition>
    
      <termination>
        <scoreAttained>0</scoreAttained>
      </termination>
      
      <constructionHeuristic>
        <constructionHeuristicType>FIRST_FIT</constructionHeuristicType>
        
          <moveFactoryClass>solution.RowChangeMoveFactory</moveFactoryClass>
        </selector>
        <acceptor>
          <completeSolutionTabuSize>1000</completeSolutionTabuSize>
        </acceptor>
        <forager>
          
        </forager>
      </localSearch>
    </solver>

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