don't try to turn null into a Point

src/cartographerFlatXY.js

@@ -8,7 +8,9 @@ import Square from './square.js';
 
 const tilePointToSquare = ({tilePoint, mapPoint, pixelPoint}) => ({
 	tile: tilePoint instanceof Square ? tilePoint : new Square(tilePoint),
-	mapTile: mapPoint instanceof Square ? mapPoint : new Square(mapPoint),
+	mapTile: mapPoint instanceof Square ? mapPoint :
+		mapPoint ? new Square(mapPoint) :
+		mapPoint,
 	pixelPoint,
 });
 

src/cartographerFlatXYZ.js

@@ -8,7 +8,9 @@ import Point from './point.js';
 
 const tilePointToHex = ({tilePoint, mapPoint, pixelPoint}) => ({
 	tile: tilePoint instanceof Hex ? tilePoint : new Hex(tilePoint),
-	mapTile: mapPoint instanceof Hex ? mapPoint : new Hex(mapPoint),
+	mapTile: mapPoint instanceof Hex ? mapPoint :
+		mapPoint ? new Hex(mapPoint) :
+		mapPoint,
 	pixelPoint,
 });
 

src/cartographerPointyXY.js

@@ -8,7 +8,9 @@ import Point from './point.js';
 
 const tilePointToSquare = ({tilePoint, mapPoint, pixelPoint}) => ({
 	tile: tilePoint instanceof Square ? tilePoint : new Square(tilePoint),
-	mapTile: mapPoint instanceof Square ? mapPoint : new Square(mapPoint),
+	mapTile: mapPoint instanceof Square ? mapPoint :
+		mapPoint ? new Square(mapPoint) :
+		mapPoint,
 	pixelPoint,
 });
 

src/cartographerPointyXYZ.js

@@ -8,7 +8,9 @@ import Point from './point.js';
 
 const tilePointToHex = ({tilePoint, mapPoint, pixelPoint}) => ({
 	tile: tilePoint instanceof Hex ? tilePoint : new Hex(tilePoint),
-	mapTile: mapPoint instanceof Hex ? mapPoint : new Hex(mapPoint),
+	mapTile: mapPoint instanceof Hex ? mapPoint :
+		mapPoint ? new Hex(mapPoint) :
+		mapPoint,
 	pixelPoint,
 });