Handle assoc into null objects.
Handle assoc into null objects.

ucscXena/ucsc-xena-client,acthp/ucsc-xena-client,ucscXena/ucsc-xena-client,ucscXena/ucsc-xena-client,acthp/ucsc-xena-client,ucscXena/ucsc-xena-client,ucscXena/ucsc-xena-client,acthp/ucsc-xena-client