fix: miner serialize/unserialize

miner.lua

@@ -30,7 +30,7 @@ local function saveMinerState()
     mission = miner.mission,
     started = miner.started,
     finished = miner.finished,
-    lastPositionState = miner.lastPositionState,
+    lastPositionState = miner.lastPositionState and textutils.serializeJSON(miner.lastPositionState),
     targetY = miner.targetY
   }
 
@@ -40,7 +40,7 @@ local function saveMinerState()
     error('saveMinerState: cannot open .minerstate file!')
   end
 
-  file.write(textutils.serialize(minerState))
+  file.write(textutils.serializeJSON(minerState))
   file.close()
 end
 
@@ -54,14 +54,20 @@ local function loadMinerState()
   local serializedMinerState = file.readAll()
   file.close()
 
-  local minerState = unserialize(serializedMinerState)
+  local minerState = textutils.unserializeJSON(serializedMinerState)
+
+  local lastPositionState = nil
+
+  if minerState.lastPositionState then
+    lastPositionState = minerState.lastPositionState
+  end
 
   miner = {
     robot = robotApi.create(minerState.robotState),
     mission = minerState.mission,
     started = minerState.started,
     finished = minerState.finished,
-    lastPositionState = minerState.lastPositionState,
+    lastPositionState = lastPositionState,
     targetY = minerState.targetY
   }
 end