Null check added to releaseAllMines.

src/engine/objects/Mine.java

@@ -130,8 +130,12 @@ public class Mine extends AbstractGameObject {
 
     public static void releaseMineClaims(PlayerCharacter playerCharacter) {
 
+        if (playerCharacter == null)
+            return;
+
         for (Mine mine : Mine.getMines()) {
 
+            if (mine.lastClaimer != null)
                 if (mine.lastClaimer.equals(playerCharacter)) {
                     mine.lastClaimer = null;
                     mine.updateGuildOwner(null);