Better JSON null validation / Disable mods on startup crash

core/src/mindustry/world/blocks/environment/ShallowLiquid.java

@@ -1,10 +1,14 @@
 package mindustry.world.blocks.environment;
 
+import arc.util.*;
 import mindustry.world.*;
 
-//do not use in mods!
+/**
+ * Do not use in mods. This class provides no new functionality, and is only used for the Mindustry sprite generator.
+ * Use the standard Floor class instead.
+ * */
 public class ShallowLiquid extends Floor{
-    public Floor liquidBase, floorBase;
+    public @Nullable Floor liquidBase, floorBase;
     public float liquidOpacity = 0.35f;
 
     public ShallowLiquid(String name){

core/src/mindustry/world/blocks/production/Drill.java

@@ -38,7 +38,7 @@ public class Drill extends Block{
     public float warmupSpeed = 0.02f;
 
     //return variables for countOre
-    protected Item returnItem;
+    protected @Nullable Item returnItem;
     protected int returnCount;
 
     /** Whether to draw the item this drill is mining. */

core/src/mindustry/world/blocks/production/GenericCrafter.java

@@ -3,6 +3,7 @@ package mindustry.world.blocks.production;
 import arc.graphics.g2d.*;
 import arc.math.*;
 import arc.struct.*;
+import arc.util.*;
 import arc.util.io.*;
 import mindustry.content.*;
 import mindustry.entities.*;
@@ -13,8 +14,8 @@ import mindustry.world.draw.*;
 import mindustry.world.meta.*;
 
 public class GenericCrafter extends Block{
-    public ItemStack outputItem;
-    public LiquidStack outputLiquid;
+    public @Nullable ItemStack outputItem;
+    public @Nullable LiquidStack outputLiquid;
 
     public float craftTime = 80;
     public Effect craftEffect = Fx.none;