Scoreboard for invalid objective shouldn't fail since objective names are not fixed and provided by players.

docs/scarpet/api/Scoreboard.md

@@ -3,7 +3,8 @@
 ### `scoreboard()`, `scoreboard(objective)`, `scoreboard(objective, key)`, `scoreboard(objective, key, value)`
 
 Displays or modifies individual scoreboard values. With no arguments, returns the list of current objectives.
-With specified `objective`, lists all keys (players) associated with current objective. With specified `objective`,
+With specified `objective`, lists all keys (players) associated with current objective, or `null` if objective does not exist.
+With specified `objective` and
 `key`, returns current value of the objective for a given player (key). With additional `value` sets a new scoreboard
  value, returning previous value associated with the `key`.
  
@@ -26,4 +27,5 @@ for the objective.
 
 ### `scoreboard_display(place, objective)`
 
-sets display location for a specified `objective`. If `objective` is `null`, then display is cleared.
+sets display location for a specified `objective`. If `objective` is `null`, then display is cleared. If objective is invalid,
+returns `null`.

src/main/java/carpet/script/api/Scoreboards.java

@@ -56,7 +56,7 @@ public class Scoreboards {
             }
             String objectiveName = lv.get(0).evalValue(c).getString();
             ScoreboardObjective objective = scoreboard.getObjective(objectiveName);
-            if (objective == null) throw new InternalExpressionException("Unknown objective: "+objectiveName);
+            if (objective == null) return LazyValue.NULL;
             if (lv.size()==1)
             {
                 Value ret = ListValue.wrap(scoreboard.getAllPlayerScores(objective).stream().map(s -> new StringValue(s.getPlayerName())).collect(Collectors.toList()));
@@ -143,7 +143,7 @@ public class Scoreboards {
             }
             String objectiveString = target.getString();
             ScoreboardObjective objective = scoreboard.getObjective(objectiveString);
-            if (objective == null) throw new InternalExpressionException("Objective doesn't exist: "+objectiveString);
+            if (objective == null) return LazyValue.NULL;
             scoreboard.setObjectiveSlot(slot, objective);
             return (_c, _t) -> new NumericValue(slot);
         });