Bug 153506 Strange error message when group key refers to bad binding column name
Run attached report design. The following error is shown: Group key "groupkey" in group 1 cannot depend on column bindings defined in the group lower than itself. This is a strange error. Since the actual problem is that the table's binding column "groupkey" is defined to refer to another existing binding: row["bad"]. EXPECTED BEHAVIOR: The error message should clearly indicate that a non-existing binding is the cause of the failure.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/impl/ExprManagerUtil.java
List bindingExprs = exprManager.getBindingExprs( );
		HashMap l = new HashMap( );
		for ( int i = 0; i < bindingExprs.size( ); i++ )
		{
			String key = ( (GroupBindingColumn) bindingExprs.get( i ) ).getGroupKey( );
			Integer groupLevel = new Integer( ( (GroupBindingColumn) bindingExprs.get( i ) ).getGroupLevel( ) );
			if ( key != null )
				l.put( groupLevel, key );
		}
		return l;
	}
	
	/**
	 *
	 */
	static class Node
	{
		private List children;
		private String value;
		/**
		 * @param value
		 */
		Node( String value )
		{
			this.value = value;
			this.children = new ArrayList( );
		}
		/**
		 * @return
		 */