HS: input_pk hot fix.

src/Model/HydraulicStructures/HydraulicStructures.py

@@ -200,7 +200,10 @@ class HydraulicStructure(SQLSubModel):
 
     @input_kp.setter
     def input_kp(self, input_kp):
-        self._input_kp = float(input_kp)
+        if input_kp is not None:
+            input_kp = float(input_kp)
+
+        self._input_kp = input_kp
         self._status.modified()
 
     @property