species_tree_node_tag does not accept NULL values
species_tree_node_tag does not accept NULL values

This happens when there are no duplication nodes: AVG() returns NULL

kumarsaurabh20/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,etapanari/ensembl-compara,etapanari/ensembl-compara,Ensembl/ensembl-compara,kumarsaurabh20/ensembl-compara,ckongEbi/ensembl-compara,danstaines/ensembl-compara,kumarsaurabh20/ensembl-compara,kumarsaurabh20/ensembl-compara,etapanari/ensembl-compara,Ensembl/ensembl-compara,danstaines/ensembl-compara,ckongEbi/ensembl-compara,Ensembl/ensembl-compara,ckongEbi/ensembl-compara,Ensembl/ensembl-compara,Ensembl/ensembl-compara,danstaines/ensembl-compara,danstaines/ensembl-compara,Ensembl/ensembl-compara,etapanari/ensembl-compara,danstaines/ensembl-compara