Problem on Get Entity Set

Hi Experts,

Have you ever got the following error message when trying to execute get EntitySet method ?

Error Info : Dereferencing the NULL reference

Class : CX_SY_REF_IS_INITIAL

My data definition :

DATA : ls_payment    TYPE zcl_zgw_ebpp_mpc=>ts_payment,

INSERT ls_payment INTO TABLE et_entityset.

initially i have 'Payment' Entity Type with Navigation Property and Association link to another Entity.

if I delete Navigation Property and Association - it works fine.

I am NOT sure if i need to define the data into something else because of navigational property and Association.

Please let me know what you think.

Thank You in advance !