Preserve empty MITC4 hidden-constraint boundary

tests/unit/analysis/hht_reduced_shell_test.cpp

@@ -1938,4 +1938,24 @@ TEST(Mitc4DrillingEvidence, DirectHiddenCertificateUsesCanonicalPrimitive) {
     EXPECT_DOUBLE_EQ(frame.hidden_velocity_defect[row], 0.0);
     EXPECT_DOUBLE_EQ(frame.hidden_acceleration_defect[row], 0.0);
   }
+  const auto accepted = frame;
+  for (const bool missing : {true, false}) {
+    auto invalid = assembly.Value();
+    if (missing)
+      invalid.hidden_constraint = fesa::Vector(0U);
+    else
+      invalid.hidden_constraint[0U] = std::numeric_limits<double>::infinity();
+    const auto rejected = fesa::hht_internal::CompleteConstraintEvidence(
+        *fixture.domain, fixture.dofs, invalid, length.Value(), null_nodes,
+        positive, tangent, &frame);
+    EXPECT_FALSE(rejected.IsOk());
+    for (const auto& pair : {
+             std::make_pair(&frame.hidden_constraint, &accepted.hidden_constraint),
+             std::make_pair(&frame.hidden_velocity_defect, &accepted.hidden_velocity_defect),
+             std::make_pair(&frame.hidden_acceleration_defect, &accepted.hidden_acceleration_defect)}) {
+      ASSERT_EQ(pair.first->Size(), pair.second->Size());
+      for (std::size_t row = 0U; row < pair.first->Size(); ++row)
+        ExpectSameBits((*pair.first)[row], (*pair.second)[row]);
+    }
+  }
 }