I tried to undestand what are you want ?
This is model of your select.
Oracle can't execute querys like this.


!-------------! ..(+) ..... !-----------! .(+) ..... !----------------!
! mwebExpense......! -----> ! Currency .....! -----> ! Null_Curr_Date ....!
!-------------! ............. !-----------! .......... !----------------!
.........! ............................................ !
........V .......................................... ! (+)
!-----------! ..................... !
! mwebwork .......!-------------
!-----------!

You, in my mind, should divide this query to set of queries and use UNION(MINES) for get result.
This is only 1 way to get result.