Fix a bug where the null buffer returned PartitionProjectionSnapshotFilter causes NPEs
Fix a bug where the null buffer returned PartitionProjectionSnapshotFilter causes NPEs

kobronson/cs-voltdb,paulmartel/voltdb,simonzhangsm/voltdb,zuowang/voltdb,VoltDB/voltdb,creative-quant/voltdb,simonzhangsm/voltdb,ingted/voltdb,paulmartel/voltdb,paulmartel/voltdb,ingted/voltdb,deerwalk/voltdb,VoltDB/voltdb,flybird119/voltdb,kobronson/cs-voltdb,zuowang/voltdb,zuowang/voltdb,creative-quant/voltdb,wolffcm/voltdb,flybird119/voltdb,kobronson/cs-voltdb,flybird119/voltdb,wolffcm/voltdb,migue/voltdb,wolffcm/voltdb,VoltDB/voltdb,migue/voltdb,ingted/voltdb,creative-quant/voltdb,paulmartel/voltdb,VoltDB/voltdb,migue/voltdb,kobronson/cs-voltdb,deerwalk/voltdb,creative-quant/voltdb,simonzhangsm/voltdb,kobronson/cs-voltdb,wolffcm/voltdb,ingted/voltdb,migue/voltdb,flybird119/voltdb,ingted/voltdb,VoltDB/voltdb,simonzhangsm/voltdb,creative-quant/voltdb,wolffcm/voltdb,simonzhangsm/voltdb,kobronson/cs-voltdb,deerwalk/voltdb,kumarrus/voltdb,kumarrus/voltdb,kumarrus/voltdb,creative-quant/voltdb,deerwalk/voltdb,flybird119/voltdb,migue/voltdb,kumarrus/voltdb,kumarrus/voltdb,wolffcm/voltdb,zuowang/voltdb,creative-quant/voltdb,migue/voltdb,deerwalk/voltdb,flybird119/voltdb,kumarrus/voltdb,creative-quant/voltdb,paulmartel/voltdb,kobronson/cs-voltdb,simonzhangsm/voltdb,ingted/voltdb,paulmartel/voltdb,VoltDB/voltdb,VoltDB/voltdb,flybird119/voltdb,migue/voltdb,kumarrus/voltdb,deerwalk/voltdb,paulmartel/voltdb,ingted/voltdb,kumarrus/voltdb,migue/voltdb,paulmartel/voltdb,zuowang/voltdb,zuowang/voltdb,kobronson/cs-voltdb,flybird119/voltdb,wolffcm/voltdb,zuowang/voltdb,deerwalk/voltdb,simonzhangsm/voltdb,zuowang/voltdb,deerwalk/voltdb,simonzhangsm/voltdb,ingted/voltdb,wolffcm/voltdb