diff --git a/src/main/java/net/minestom/server/instance/BlockModifier.java b/src/main/java/net/minestom/server/instance/BlockModifier.java
index d11fb1eff..f1bae62d6 100644
--- a/src/main/java/net/minestom/server/instance/BlockModifier.java
+++ b/src/main/java/net/minestom/server/instance/BlockModifier.java
@@ -23,10 +23,13 @@ public interface BlockModifier {
     }
 
     default void setBlock(BlockPosition blockPosition, Block block) {
+        Check.notNull(blockPosition, "The block position cannot be null");
+        Check.notNull(block, "The block cannot be null");
         setBlock(blockPosition.getX(), blockPosition.getY(), blockPosition.getZ(), block);
     }
 
     default void setBlockStateId(BlockPosition blockPosition, short blockStateId) {
+        Check.notNull(blockPosition, "The block position cannot be null");
         setBlockStateId(blockPosition.getX(), blockPosition.getY(), blockPosition.getZ(), blockStateId);
     }
 
@@ -49,6 +52,7 @@ public interface BlockModifier {
     }
 
     default void setCustomBlock(BlockPosition blockPosition, String customBlockId) {
+        Check.notNull(blockPosition, "The block position cannot be null");
         setCustomBlock(blockPosition.getX(), blockPosition.getY(), blockPosition.getZ(), customBlockId);
     }
 
@@ -58,4 +62,9 @@ public interface BlockModifier {
         setSeparateBlocks(x, y, z, blockStateId, customBlockId, null);
     }
 
+    default void setSeparateBlocks(BlockPosition blockPosition, short blockStateId, short customBlockId) {
+        Check.notNull(blockPosition, "The block position cannot be null");
+        setSeparateBlocks(blockPosition.getX(), blockPosition.getY(), blockPosition.getZ(), blockStateId, customBlockId, null);
+    }
+
 }
diff --git a/src/main/java/net/minestom/server/timer/SchedulerManager.java b/src/main/java/net/minestom/server/timer/SchedulerManager.java
index c8bdad954..375baadc0 100644
--- a/src/main/java/net/minestom/server/timer/SchedulerManager.java
+++ b/src/main/java/net/minestom/server/timer/SchedulerManager.java
@@ -12,6 +12,7 @@ import java.util.concurrent.atomic.AtomicInteger;
  */
 public class SchedulerManager {
 
+    private boolean instanced;
     // A counter for all normal tasks
     private final AtomicInteger counter;
     // A counter for all shutdown tasks
@@ -29,6 +30,11 @@ public class SchedulerManager {
      * Default constructor
      */
     public SchedulerManager() {
+        if (instanced) {
+            throw new IllegalStateException("You cannot instantiate a SchedulerManager," +
+                    " use MinecraftServer.getSchedulerManager()");
+        }
+        this.instanced = true;
         this.counter = new AtomicInteger();
         this.shutdownCounter = new AtomicInteger();