Unable to build expression for 'inline-eval' when using Lists of objects

If a Rule has a .size== in when and the variable is an Object, then we get the following:-
Unable to build expression for 'inline-eval' : [Error: incompatible types in statement: class java.lang.Integer (compared from: class droolstesting.SubType)]

Full example:

Rule:

package droolstesting

rule "rule2"
dialect "mvel"
when
$m : MyItem(items!=null || items.size == 0)
then
System.out.println("Got 0");
retract($m)
end

MyItems.java:

package droolstesting;

import java.util.ArrayList;
import java.util.List;

public class MyItem {
int number=0;
String string="empty";

List<SubType> items=new ArrayList<SubType>();

public List<SubType> getItems()

{ return items; }

public void setItems(List<SubType> items)

{ this.items = items; }

public int getNumber()

{ return number; }

public void setNumber(int number)

{ this.number = number; }

public String getString()

{ return string; }

public void setString(String string)

{ this.string = string; }

}

SubType.java:
package droolstesting;
public class SubType {
String name="";

}

Main.java:
package droolstesting;

import java.io.File;
import java.io.IOException;
import org.drools.compiler.DroolsParserException;
import org.drools.compiler.PackageBuilder;
import org.drools.io.ResourceFactory;

/**
*

• @author richarda
  */
  public class Main {

/**

• @param args the command line arguments
  */
  public static void main(String[] args) throws IOException, DroolsParserException
  Unknown macro: { PackageBuilder pkgBuilder = new PackageBuilder(); pkgBuilder.addPackageFromDrl(ResourceFactory.newClassPathResource("rule1.drl")); if (pkgBuilder.hasErrors()) { System.err.println(pkgBuilder.getErrors().toString()); throw new RuntimeException("Unable to compile rules"); }
  pkgBuilder.addPackageFromDrl(ResourceFactory.newClassPathResource("rule2.drl"));
  if (pkgBuilder.hasErrors()) { System.err.println(pkgBuilder.getErrors().toString()); throw new RuntimeException("Unable to compile rules"); } }

  }

Result:

run:
Unable to build expression for 'inline-eval' : [Error: incompatible types in statement: class java.lang.Integer (compared from: class droolstesting.SubType)]
[Near :

{... items != null || items.size == 0 ....}]
^
[Line: 6, Column: 14]'items != null || items.size == 0'
[Error: incompatible types in statement: class java.lang.Integer (compared from: class droolstesting.SubType)]
[Near : {... items != null || items.size == 0 ....}

]
^
[Line: 6, Column: 14] : [Rule name='rule2']
[Error: incompatible types in statement: class java.lang.Integer (compared from: class droolstesting.SubType)]
[Near :

{... items != null || items.size == 0 ....}

]
^
[Line: 1, Column: 18]

Exception in thread "main" java.lang.RuntimeException: Unable to compile rules
at droolstesting.Main.main(Main.java:32)
Java Result: 1
BUILD SUCCESSFUL (total time: 1 second)