Problem in modifying OFDM transmitter block (v3.8)

Dear Community, 

I am trying to modify the OFDM transmitter block by adding one more payload modulation (16-QAM).  In the python file, I added the following line in the "def_get_constellation (bps)" section as well as edited the yml file respectively and it's built successfully.

" digital.constellation_16qam() "

But when I try to use this block with 16QAM modulation in the example OFDM grc file, it says "Modulation not supported". Though, BPSK, QPSK work fine with the same new block. 

Am I missing something? Waiting for your suggestions.

Thank you.

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Regards,

Rupak Paul