SUMMARY:
I am getting a NPE when using modify() with a JavaBean that implements PropertyChangeSupport. 
 
I have included the original source and a proposed fix.  Stack trace is also included.
 
This applies to Drools 5.0.1, and has been verified to also be a problem for 5.1.0.M1.
 
 
DETAIL:
 
I have a rule that looks like this:
 

rule "Constrain to owner or published to public"

when

  $fact : ListFact(

  path not matches ".*owner.*",

  noopResponse == true

)

then

  modify($fact)

  {

    setPath( "[owner/username='' or publishlist/publish='All Users']")

  }

end

 
The $fact is a JavaBean that implements PropertyChangeSupport, and I've verified that everything is working correctly at the bean level.  When I run this rule, I get this exception:
 
Caused by: java.lang.NullPointerException:
        at org.drools.common.EqualityKey.removeFactHandle(EqualityKey.java:109)
        at org.drools.common.AbstractWorkingMemory.update(AbstractWorkingMemory.java:1435)
        at org.drools.common.AbstractWorkingMemory.update(AbstractWorkingMemory.java:1350)
        at org.drools.common.AbstractWorkingMemory.propertyChange(AbstractWorkingMemory.java:1577)
        at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:339)
        at java.beans.PropertyChangeSupport.firePropertyChange(PropertyChangeSupport.java:276)
        at com.infotrustgroup.rules.RestFact.setPath(RestFact.java:264)
        at com.infotrustgroup.facts.ParametersFact.setPath(ParametersFact.java:105)
        at com.infotrustgroup.facts.ParametersFact.setPath(ParametersFact.java:74)
        at com.infotrustgroup.what.Rule_Constrain_to_owner_or_published_to_public_0.consequence(Rule_Constrain_to_owner_or_published_to_public_0.java:12)
        at com.infotrustgroup.what.Rule_Constrain_to_owner_or_published_to_public_0ConsequenceInvoker.evaluate(Rule_Constrain_to_owner_or_published_to_public_0ConsequenceInvoker.java:23)
        at org.drools.common.DefaultAgenda.fireActivation(DefaultAgenda.java:934)
        ... 38 more
 
The offending line is marked below.  It looks like maybe "this.instances" is null in the "else" clause.
 
    public void removeFactHandle(final InternalFactHandle handle) {
        if ( this.handle == handle ) {
            if ( this.instances == null ) {
                this.handle = null;
            } else {
                this.handle = (InternalFactHandle) this.instances.remove( 0 );
                if ( this.instances.isEmpty() ) {
                    this.instances = null;
                }
            }
        } else {
            ***this.instances.remove( handle );***
            if ( this.instances.isEmpty() ) {
                this.instances = null;
            }
        }
    }
 
It looks like someone else ran into this problem before, but only fixed it for the "if" portion, not the "else" portion.  I modified the code as follows, and this seems to fix the NPE.  Basically, I followed the pattern from the "if" portion.
 
    public void removeFactHandle(final InternalFactHandle handle) {
        if ( this.handle == handle ) {
            if ( this.instances == null ) {
                this.handle = null;
            } else {
                this.handle = (InternalFactHandle) this.instances.remove( 0 );
                if ( this.instances.isEmpty() ) {
                    this.instances = null;
                }
            }
        } else {
   if(this.instances == null)
   {
    this.handle = null;
   }
   else
   {
    this.instances.remove( handle );
    if ( this.instances.isEmpty() ) {
     this.instances = null;
    }
   }
        }
    }
Please read around the formatting.  Can someone verify if this is a correct fix, and if it should be applied to the codebase?  It seems to work for me.  It does not break any unit tests in drools-core 5.0.1 either.
 

Jason Smith
Software Engineer
InfoTrust Group, Inc.

500 Discovery Parkway, Suite 200
Superior, CO 80027
Office 303-627-6571
Fax 303-666-6711
Email jsmith@infotrustgroup.com

WEB www.infotrustgroup.com

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