added "none" as a possible return value of getCoordinateDisplaySystem

src/Goban/CanvasRenderer.ts

@@ -2822,6 +2822,8 @@ export class GobanCanvas extends Goban implements GobanCanvasInterface {
                         place("" + (c + 1), x, y);
                     }
                     break;
+                case "none":
+                    break;
             }
         };
 
@@ -2878,6 +2880,8 @@ export class GobanCanvas extends Goban implements GobanCanvasInterface {
                         v_place(chinese_japanese_numbers[c], x, y);
                     }
                     break;
+                case "none":
+                    break;
             }
         };
 

src/Goban/InteractiveBase.ts

@@ -464,7 +464,7 @@ export abstract class GobanInteractive extends GobanBase {
         return ret;
     }
 
-    protected getCoordinateDisplaySystem(): "A1" | "1-1" {
+    protected getCoordinateDisplaySystem(): "A1" | "1-1" | "none" {
         if (callbacks.getCoordinateDisplaySystem) {
             return callbacks.getCoordinateDisplaySystem();
         }

src/Goban/callbacks.ts

@@ -19,7 +19,7 @@ import { GobanSelectedThemes } from "./Goban";
 
 export interface GobanCallbacks {
     defaultConfig?: () => any;
-    getCoordinateDisplaySystem?: () => "A1" | "1-1";
+    getCoordinateDisplaySystem?: () => "A1" | "1-1" | "none";
     isAnalysisDisabled?: (goban: GobanBase, perGameSettingAppliesToNonPlayers: boolean) => boolean;
 
     getClockDrift?: () => number;