Updates the solver to handle an empty problem.

Author: mmoffitt

src/solver.cc

@@ -81,6 +81,7 @@ class SolverImpl {
       backtracks_(*backtracks), cancelled_(cancelled) {}
 
   absl::StatusOr<Solution> Solve() {
+    if (problem_.buffers.empty()) return solution_;
     const auto num_buffers = problem_.buffers.size();
     assignment_.offsets.resize(num_buffers, kNoOffset);
     solution_.offsets.resize(num_buffers, kNoOffset);

tests/solver_test.cc

@@ -137,6 +137,11 @@ TEST_P(SolverTest, InfeasibleTricky) {
   test_infeasible(problem);
 }
 
+TEST_P(SolverTest, EmptyProblem) {
+  const Problem problem;
+  test_feasible(problem);
+}
+
 TEST_P(SolverTest, SingleBuffer) {
   const Problem problem = {
     .buffers = {{.lifespan = {0, 2}, .size = 2}},