NPE when imports not available

REPORTED BY DIRK BERGSTROM:
------------------------------------------------

Trying to compile this rule, I get an NPE:

package foo;
rule "Generates NPE"
when
$count : Thing( size > 0 ) from collect( Gizmo( length == 1 ) )
then
System.out.println("boo");
end

Like so:

java.lang.NullPointerException
at org.drools.rule.Rule.addDeclarations(Rule.java:316)
at org.drools.rule.Rule.addPattern(Rule.java:304)
at org.drools.semantics.java.RuleBuilder.build(RuleBuilder.java:320)
at org.drools.semantics.java.RuleBuilder.build(RuleBuilder.java:215)
at org.drools.compiler.PackageBuilder.addRule(PackageBuilder.java:366)
at org.drools.compiler.PackageBuilder.addPackage(PackageBuilder.java:215)
at org.drools.compiler.PackageBuilder.addPackageFromDrl(PackageBuilder.java:181)
at net.juniper.dash.DroolsTest.readRule(DroolsTest.java:106)
at net.juniper.dash.DroolsTest.main(DroolsTest.java:22)

This happens when there are two undefined classes referenced in a rule, with the
second one inside a collect() statement. If I import Thing, or import Gizmo, or
have a constraint on Gizmo not in a collect(), I get a parser exception, as
expected.

This is with Trunk, revision 8110.