there should be a context node at your view level. Please check ON NEW FOCUS method is implemented or not.
If not, you can implement that method with below code.
DATA: lv_collection TYPE REF TO if_bol_bo_col,
entity TYPE REF TO cl_crm_bol_entity.
* get collection of dependent nodes
entity ?= focus_bo.
TRY.
lv_collection = entity->get_related_entities(
iv_relation_name = 'BTHeaderCustExt' ).
IF lv_collection IS NOT BOUND or lv_collection->size( ) = 0.
IF entity->is_changeable( ) = ABAP_TRUE.
TRY.
entity = entity->create_related_entity(
iv_relation_name = 'BTHeaderCustExt' ).
CATCH cx_crm_genil_model_error cx_crm_genil_duplicate_rel.
* should never happen
ENDTRY.
IF entity IS BOUND.
CREATE OBJECT lv_collection TYPE cl_crm_bol_bo_col.
lv_collection->add( entity ).
ENDIF.
ENDIF.
ENDIF.
CATCH cx_crm_genil_model_error.
* should never happen
EXIT.
CATCH cx_sy_ref_is_initial.
ENDTRY.
me->set_collection( lv_collection ).