bugfix for get_ready_data_nodes handling missing data
bugfix for get_ready_data_nodes handling missing data

StanfordBioinformatics/xppf,StanfordBioinformatics/loom,StanfordBioinformatics/loom,StanfordBioinformatics/loom,StanfordBioinformatics/xppf,StanfordBioinformatics/xppf,StanfordBioinformatics/xppf,StanfordBioinformatics/loom