Bug 202891 NPE throws out when click on data item in layout[0001]
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/internal/ui/dialogs/BindingDialogHelper.java
this.messageLine.setImage( PlatformUI.getWorkbench( )
							.getSharedImages( )
							.getImage( ISharedImages.IMG_OBJS_ERROR_TSK ) );
					return;
				}
			}
		}
		this.messageLine.setText( "" ); 
		this.messageLine.setImage( null );
		if ( txtExpression != null
				&& ( txtExpression.getText( ) == null || txtExpression.getText( )
						.trim( )
						.equals( "" ) ) ) 
		{
			if ( dialog.getOkButton( ) != null )
			{
				dialog.getOkButton( ).setEnabled( false );
				return;
			}
		}
		if ( cmbDataField != null
				&& ( cmbDataField.getText( ) == null || cmbDataField.getText( )
						.trim( )
						.equals( "" ) ) && cmbDataField.isEnabled( ) ) 
		{
			if ( dialog.getOkButton( ) != null )
			{
				dialog.getOkButton( ).setEnabled( false );
				return;
			}