Forms :: Close A Window In Query Mode

How do I close a window in query mode?My form has a button "Populate from Charge Master" which opens a window containing a List Item (Department Names) and 2 buttons,

1. "Select the Dept" and
2. "Cancel"

The WHEN-BUTTON-PRESSED trigger code for "Populate from Charge Master" button is as follows:

begin
SHOW_WINDOW('WINDOW_POP_FROM_CHARGE_MASTER');
go_block('bl_med_dep');
enter_query;
end;

Code for "Select" button in the window is:

populate_from_charge_master(:bl_med_dep.med_dep_code,:bl_med_charge_party.charge_party_no);
execute_query;
COMMIT;
HIDE_WINDOW('WINDOW_POP_FROM_CHARGE_MASTER');
GO_BLOCK('BL_MED_CHARGE_PARTY');
EXECUTE_QUERY;

Code for "Cancel" button in the window is:

BEGIN
hide_window('WINDOW_POP_FROM_CHARGE_MASTER');
show_window('WINDOW1');
GO_BLOCK('BL_CHARGE_COMPANY');
END;

Here WINDOW1 is the main window and WINDOW_POP_FROM_CHARGE_MASTER is the window which must be closed when "Cancel" button is pressed.

When I remove "enter_query" statement in "populate from charge master" trigger code, I am not able to select any of the departments from the list. and If I have that statement, I am not able to hide/close the window.