Need help on server expression for to_date function - Demantra

I am having this business requirement, where they want to have a series which contains the data from 2 different series based on the time.

Attached is the New series requirement example

I am using the below server expression, but it is not giving me the desired result.

The issue is only with the data populated for Dec-2015 month. For rest of the months the data is coming up correct.

sum(decode(sign((branch_data.sales_date) - to_date(get_max_date,'mm/dd/yyyy hh24:mi:ss')),-1, nvl(branch_data.actual_quantity, 0),0, nvl(branch_data.xxdm_final_fcst_lag1,0), nvl(branch_data.xxdm_final_fcst_lag1,0)))