Represent Assigned PI as an optional<>

Suggested by: [at]joakim-hove

opm/parser/eclipse/EclipseState/Schedule/Well/Well.hpp

@@ -23,9 +23,9 @@
 
 #include <cstddef>
 #include <iosfwd>
-#include <limits>
 #include <map>
 #include <memory>
+#include <optional>
 #include <string>
 #include <utility>
 #include <vector>
@@ -633,7 +633,7 @@ private:
     double solvent_fraction;
     bool has_produced = false;
     bool prediction_mode = true;
-    double productivity_index{ std::numeric_limits<double>::lowest() };
+    std::optional<double> productivity_index{ std::nullopt };
 
     std::shared_ptr<WellEconProductionLimits> econ_limits;
     std::shared_ptr<WellFoamProperties> foam_properties;

src/opm/parser/eclipse/EclipseState/Schedule/Well/Well.cpp

@@ -816,7 +816,7 @@ void Well::applyWellProdIndexScaling(const double currentEffectivePI) {
         // No connections for this well.  Unexpected.
         return;
 
-    if (this->productivity_index < 0.0)
+    if (!this->productivity_index)
         // WELPI not activated.  Nothing to do.
         return;
 
@@ -824,7 +824,7 @@ void Well::applyWellProdIndexScaling(const double currentEffectivePI) {
         // No change in scaling.
         return;
 
-    this->connections->applyWellPIScaling(this->productivity_index / currentEffectivePI);
+    this->connections->applyWellPIScaling(*this->productivity_index / currentEffectivePI);
 }
 
 const WellConnections& Well::getConnections() const {