Upgrade templates: PP, AP as string.

source/module/items/M5Item.ts

@@ -236,4 +236,17 @@ export class M5Item extends Item {
 		return (this as any).getEmbeddedDocument("Item", itemId)
 	}
 
+	override migrateSystemData(): any {
+		const item = (this as any)
+		const data = item.system
+
+		if (item.type === "spell") {
+			if (typeof data.ap !== "string") {
+				data.ap = Number.isFinite(data.ap) ? "" + data.ap : ""
+			}
+		}
+
+		return super.migrateSystemData()
+	}
+
 }