Bug 168026 Still use the existing data binding even though the aggregate is different
I had a table in which a data binding which aggregates on a group. When I insert a new data item in the report, although the expressions are same, it aggregates on All, then it refered to the existing data binding. The expected behavior would be a new data binding is created with different aggregates.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/api/ScalarParameterHandle.java
*/
	public boolean allowNull( )
	{
		return getBooleanProperty( ALLOW_NULL_PROP );
	}
	/**
	 * Sets the flag that indicates whether the value of the parameter can be
	 * <code>null</code>.
	 * 
	 * @param allowNull
	 *            <code>true</code> if the value can be <code>null</code>,
	 *            <code>false</code> if the value can not be <code>null</code>.
	 * @throws SemanticException
	 *             if the property is locked.
	 */
	public void setAllowNull( boolean allowNull ) throws SemanticException
	{
		setProperty( ALLOW_NULL_PROP, Boolean.valueOf( allowNull ) );
	}
	/**
	 * Tests whether the string value of the parameter can be <code>null</code>.
	 * 
	 * @return <code>true</code> if the value can be <code>null</code>,
	 *         <code>false</code> if the value can not be <code>null</code>.
	 */
	public boolean allowBlank( )
	{
		return getBooleanProperty( ALLOW_BLANK_PROP );
	}
	/**