From b886f1ddbcfff84a760313b98fc4c33fc8b202b3 Mon Sep 17 00:00:00 2001
From: Laurent Perron <lperron@google.com>
Date: Thu, 16 May 2019 11:45:46 +0200
Subject: [PATCH] fix ShiftSchedulingSat.cs; improve linear code in CP-SAT C#
 to make it more robust

---
 examples/dotnet/ShiftSchedulingSat.cs    | 7 +++----
 ortools/sat/csharp/IntegerExpressions.cs | 9 ++++++---
 2 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/examples/dotnet/ShiftSchedulingSat.cs b/examples/dotnet/ShiftSchedulingSat.cs
index 9a46d717af..2a06adb572 100644
--- a/examples/dotnet/ShiftSchedulingSat.cs
+++ b/examples/dotnet/ShiftSchedulingSat.cs
@@ -197,7 +197,7 @@ public class ShiftSchedulingSat
             {
                 foreach (int w in Range(numWeeks))
                 {
-                    var works = new IntVar[numDays];
+                    var works = new IntVar[7];
 
                     foreach (int d in Range(7))
                     {
@@ -284,10 +284,9 @@ public class ShiftSchedulingSat
 
         // Solve model
         var solver = new CpSolver();
-	solver.StringParameters = "num_search_workers:8";
+	    solver.StringParameters = "num_search_workers:8, log_search_progress: true";
 
-        var solutionPrinter = new ObjectiveSolutionPrinter();
-        var status = solver.SolveWithSolutionCallback(model, solutionPrinter);
+        var status = solver.Solve(model);
 
         // Print solution
         if (status == CpSolverStatus.Optimal || status == CpSolverStatus.Feasible)
diff --git a/ortools/sat/csharp/IntegerExpressions.cs b/ortools/sat/csharp/IntegerExpressions.cs
index 278a0558ab..1f7d1f48af 100644
--- a/ortools/sat/csharp/IntegerExpressions.cs
+++ b/ortools/sat/csharp/IntegerExpressions.cs
@@ -223,8 +223,10 @@ namespace Google.OrTools.Sat
     {
       List<LinearExpr> exprs = new List<LinearExpr>();
       List<long> coeffs = new List<long>();
-      exprs.Add(e);
-      coeffs.Add(initial_coeff);
+      if ((Object)e != null) {
+        exprs.Add(e);
+        coeffs.Add(initial_coeff);
+      }
       long constant = 0;
 
       while (exprs.Count > 0)
@@ -233,7 +235,7 @@ namespace Google.OrTools.Sat
         exprs.RemoveAt(0);
         long coeff = coeffs[0];
         coeffs.RemoveAt(0);
-        if (coeff == 0) continue;
+        if (coeff == 0 || (Object)expr == null) continue;
 
         if (expr is ProductCst)
         {
@@ -468,6 +470,7 @@ namespace Google.OrTools.Sat
       for (int i = 0; i < expressions_.Length; ++i)
       {
         LinearExpr expr = expressions_[i];
+        if ((Object)expr == null) continue;
         long coeff = coefficients_[i];
         if (i != 0)
         {