Do not visit null values in StackIndirectReferenceTable
Do not visit null values in StackIndirectReferenceTable

Change-Id: Ib76b9f6d27b265a35eea3ed69e2f495ed4e3df88

treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst