Exception in thread "main" java.lang.NullPointerException
        at edu.cmu.tetrad.graph.EdgeListGraph.addEdge(EdgeListGraph.java:1139)
        at edu.cmu.tetrad.search.FgesMb.addUnconditionalArrows(FgesMb.java:373)
        at edu.cmu.tetrad.search.FgesMb.calcDConnections(FgesMb.java:290)
        at edu.cmu.tetrad.search.FgesMb.search(FgesMb.java:229)
        at edu.cmu.tetrad.algcomparison.algorithm.oracle.cpdag.FgesMb.search(FgesMb.java:67)
        at edu.pitt.dbmi.causal.cmd.tetrad.TetradRunner.lambda$runSearch$3(TetradRunner.java:203)
        at java.base/java.lang.Iterable.forEach(Iterable.java:75)
        at edu.pitt.dbmi.causal.cmd.tetrad.TetradRunner.runSearch(TetradRunner.java:202)
        at edu.pitt.dbmi.causal.cmd.tetrad.TetradRunner.runAlgorithm(TetradRunner.java:119)
        at edu.pitt.dbmi.causal.cmd.CausalCmdApplication.runTetrad(CausalCmdApplication.java:149)
        at edu.pitt.dbmi.causal.cmd.CausalCmdApplication.main(CausalCmdApplication.java:113)