SPIGOT-2540: Add nullability annotations to entire Bukkit API

By: Darkyenus <darkyenus@gmail.com>

paper-api/src/main/java/org/bukkit/entity/minecart/CommandMinecart.java

@@ -1,6 +1,8 @@
 package org.bukkit.entity.minecart;
 
 import org.bukkit.entity.Minecart;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 public interface CommandMinecart extends Minecart {
 
@@ -11,6 +13,7 @@ public interface CommandMinecart extends Minecart {
      *
      * @return Command that this CommandMinecart will run when powered.
      */
+    @NotNull
     public String getCommand();
 
     /**
@@ -21,7 +24,7 @@ public interface CommandMinecart extends Minecart {
      * @param command Command that this CommandMinecart will run when
      *     activated.
      */
-    public void setCommand(String command);
+    public void setCommand(@Nullable String command);
 
     /**
      * Sets the name of this CommandMinecart.  The name is used with commands
@@ -30,6 +33,6 @@ public interface CommandMinecart extends Minecart {
      *
      * @param name New name for this CommandMinecart.
      */
-    public void setName(String name);
+    public void setName(@Nullable String name);
 
 }