Non null user methods (#1856)

* This makes some User methods non-null.

Instead of returning null, some methods will throw an error if they are
called on non-Players. This means code does not have to do null checks.

* Perform null check in method.

src/main/java/world/bentobox/bentobox/api/commands/admin/blueprints/AdminBlueprintCommand.java

@@ -70,15 +70,16 @@ protected void showClipboard(User user) {
 
             if (clipboards.containsKey(user.getUniqueId())) {
                 BlueprintClipboard clipboard = clipboards.get(user.getUniqueId());
-                if (clipboard.getPos1() != null && clipboard.getPos2() != null) {
-                    paintAxis(user, clipboard);
-                }
+                paintAxis(user, clipboard);
             }
 
         }, 20, 20));
     }
 
     private void paintAxis(User user, BlueprintClipboard clipboard) {
+        if (clipboard.getPos1() == null || clipboard.getPos2() == null) {
+            return;
+        }
         int minX = Math.min(clipboard.getPos1().getBlockX(), clipboard.getPos2().getBlockX());
         int minY = Math.min(clipboard.getPos1().getBlockY(), clipboard.getPos2().getBlockY());
         int minZ = Math.min(clipboard.getPos1().getBlockZ(), clipboard.getPos2().getBlockZ());

src/main/java/world/bentobox/bentobox/api/user/User.java

@@ -4,6 +4,7 @@
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.Objects;
 import java.util.Optional;
 import java.util.Set;
 import java.util.UUID;
@@ -175,16 +176,17 @@ public Set<PermissionAttachmentInfo> getEffectivePermissions() {
         return sender.getEffectivePermissions();
     }
 
-    @Nullable
+    @NonNull
     public PlayerInventory getInventory() {
-        return player != null ? player.getInventory() : null;
+        return Objects.requireNonNull(player, "getInventory can only be called for online players!").getInventory();
     }
 
-    @Nullable
+    @NonNull
     public Location getLocation() {
-        return player != null ? player.getLocation() : null;
+        return Objects.requireNonNull(player, "getLocation can only be called for online players!").getLocation();
     }
 
+    @NonNull
     public String getName() {
         return player != null ? player.getName() : plugin.getPlayers().getName(playerUUID);
     }