diff --git a/Bukkit/src/main/java/com/github/intellectualsites/plotsquared/bukkit/object/BukkitPlayer.java b/Bukkit/src/main/java/com/github/intellectualsites/plotsquared/bukkit/object/BukkitPlayer.java
index 60c1351d0..888de164a 100644
--- a/Bukkit/src/main/java/com/github/intellectualsites/plotsquared/bukkit/object/BukkitPlayer.java
+++ b/Bukkit/src/main/java/com/github/intellectualsites/plotsquared/bukkit/object/BukkitPlayer.java
@@ -19,6 +19,7 @@ import org.bukkit.event.player.PlayerTeleportEvent.TeleportCause;
 import org.bukkit.permissions.PermissionAttachmentInfo;
 import org.bukkit.plugin.RegisteredListener;
 
+import javax.annotation.Nonnull;
 import java.util.Arrays;
 import java.util.Set;
 import java.util.UUID;
@@ -53,7 +54,7 @@ public class BukkitPlayer extends PlotPlayer {
         return location == null ? BukkitUtil.getLocation(this.player) : location;
     }
 
-    @Override public UUID getUUID() {
+    @Nonnull @Override public UUID getUUID() {
         if (this.uuid == null) {
             this.uuid = UUIDHandler.getUUID(this);
         }
diff --git a/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/database/AbstractDB.java b/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/database/AbstractDB.java
index ae4a1fa76..0eecd6539 100644
--- a/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/database/AbstractDB.java
+++ b/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/database/AbstractDB.java
@@ -4,6 +4,7 @@ import com.github.intellectualsites.plotsquared.plot.flag.Flag;
 import com.github.intellectualsites.plotsquared.plot.object.*;
 import com.github.intellectualsites.plotsquared.plot.object.comment.PlotComment;
 
+import javax.annotation.Nonnull;
 import java.util.*;
 
 public interface AbstractDB {
@@ -300,7 +301,7 @@ public interface AbstractDB {
      *
      * @param plot The Plot to get comments from
      */
-    void getComments(Plot plot, String inbox, RunnableVal<List<PlotComment>> whenDone);
+    void getComments(@Nonnull Plot plot, String inbox, RunnableVal<List<PlotComment>> whenDone);
 
     void createPlotAndSettings(Plot plot, Runnable whenDone);
 
diff --git a/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/database/SQLManager.java b/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/database/SQLManager.java
index 2995a448d..876a29121 100644
--- a/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/database/SQLManager.java
+++ b/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/database/SQLManager.java
@@ -13,6 +13,7 @@ import com.github.intellectualsites.plotsquared.plot.util.StringMan;
 import com.github.intellectualsites.plotsquared.plot.util.TaskManager;
 import com.google.common.base.Charsets;
 
+import javax.annotation.Nonnull;
 import java.sql.*;
 import java.text.ParseException;
 import java.text.SimpleDateFormat;
@@ -2168,7 +2169,7 @@ import java.util.concurrent.atomic.AtomicInteger;
         });
     }
 
-    @Override public void getComments(final Plot plot, final String inbox,
+    @Override public void getComments(@Nonnull Plot plot, final String inbox,
         final RunnableVal<List<PlotComment>> whenDone) {
         addPlotTask(plot, new UniqueStatement("getComments_" + plot) {
             @Override public void set(PreparedStatement statement) throws SQLException {
diff --git a/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/object/ConsolePlayer.java b/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/object/ConsolePlayer.java
index 18a0ce7bc..6f386b3cb 100644
--- a/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/object/ConsolePlayer.java
+++ b/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/object/ConsolePlayer.java
@@ -6,6 +6,7 @@ import com.github.intellectualsites.plotsquared.plot.database.DBFunc;
 import com.github.intellectualsites.plotsquared.plot.util.PlotGameMode;
 import com.github.intellectualsites.plotsquared.plot.util.PlotWeather;
 
+import javax.annotation.Nonnull;
 import java.util.UUID;
 
 public class ConsolePlayer extends PlotPlayer {
@@ -45,7 +46,7 @@ public class ConsolePlayer extends PlotPlayer {
         return getLocation();
     }
 
-    @Override public UUID getUUID() {
+    @Nonnull @Override public UUID getUUID() {
         return DBFunc.EVERYONE;
     }
 
diff --git a/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/object/Plot.java b/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/object/Plot.java
index 23f561233..fd76d9c87 100644
--- a/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/object/Plot.java
+++ b/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/object/Plot.java
@@ -21,6 +21,7 @@ import com.google.common.collect.BiMap;
 import com.google.common.collect.ImmutableSet;
 import com.sk89q.jnbt.CompoundTag;
 
+import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.awt.geom.Area;
 import java.awt.geom.PathIterator;
@@ -322,7 +323,7 @@ public class Plot {
      * @param uuid the player uuid
      * @return if the provided uuid is the owner of the plot
      */
-    public boolean isOwner(UUID uuid) {
+    public boolean isOwner(@Nonnull UUID uuid) {
         if (uuid.equals(this.owner)) {
             return true;
         }
@@ -339,6 +340,9 @@ public class Plot {
 
     /**
      * Gets a immutable set of owner UUIDs for a plot (supports multi-owner mega-plots).
+     * <p>
+     * This method cannot be used to add or remove owners from a plot.
+     * </p>
      *
      * @return the plot owners
      */
@@ -752,8 +756,9 @@ public class Plot {
     public boolean setOwner(UUID owner, PlotPlayer initiator) {
         boolean result = EventUtil.manager
             .callOwnerChange(initiator, this, owner, hasOwner() ? this.owner : null, hasOwner());
-        if (!result)
+        if (!result) {
             return false;
+        }
         if (!hasOwner()) {
             this.owner = owner;
             create();
@@ -948,8 +953,9 @@ public class Plot {
      * @param name name
      */
     public void setSign(final String name) {
-        if (!isLoaded())
+        if (!isLoaded()) {
             return;
+        }
         if (!PlotSquared.get().isMainThread(Thread.currentThread())) {
             TaskManager.runTask(() -> Plot.this.setSign(name));
             return;
@@ -1165,8 +1171,9 @@ public class Plot {
         Location bot = corners[1];
         Location loc = new Location(this.getWorldName(), MathMan.average(bot.getX(), top.getX()),
             MathMan.average(bot.getY(), top.getY()), MathMan.average(bot.getZ(), top.getZ()));
-        if (!isLoaded())
+        if (!isLoaded()) {
             return loc;
+        }
         int y =
             isLoaded() ? WorldUtil.IMP.getHighestBlock(getWorldName(), loc.getX(), loc.getZ()) : 62;
         if (area.ALLOW_SIGNS) {
@@ -1201,8 +1208,9 @@ public class Plot {
             Location bot = this.getBottomAbs();
             Location loc = new Location(bot.getWorld(), bot.getX() + home.x, bot.getY() + home.y,
                 bot.getZ() + home.z, home.yaw, home.pitch);
-            if (!isLoaded())
+            if (!isLoaded()) {
                 return loc;
+            }
             if (!WorldUtil.IMP.getBlock(loc).isAir()) {
                 loc.setY(Math.max(
                     1 + WorldUtil.IMP.getHighestBlock(this.getWorldName(), loc.getX(), loc.getZ()),
@@ -1514,6 +1522,7 @@ public class Plot {
     }
 
     //TODO Better documentation needed.
+
     /**
      * Return the top location for the plot.
      *
@@ -1526,6 +1535,7 @@ public class Plot {
     }
 
     //TODO Better documentation needed.
+
     /**
      * Return the bottom location for the plot.
      */
@@ -2616,7 +2626,6 @@ public class Plot {
     }
 
     /**
-     *
      * Do the plot entry tasks for each player in the plot<br>
      * - Usually called when the plot state changes (unclaimed/claimed/flag change etc)
      */
diff --git a/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/object/PlotPlayer.java b/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/object/PlotPlayer.java
index c0d9ec726..b3df60558 100644
--- a/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/object/PlotPlayer.java
+++ b/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/object/PlotPlayer.java
@@ -14,6 +14,7 @@ import com.github.intellectualsites.plotsquared.plot.util.*;
 import com.github.intellectualsites.plotsquared.plot.util.expiry.ExpireManager;
 import lombok.NonNull;
 
+import javax.annotation.Nonnull;
 import java.nio.ByteBuffer;
 import java.util.*;
 import java.util.concurrent.ConcurrentHashMap;
@@ -326,7 +327,7 @@ public abstract class PlotPlayer implements CommandCaller, OfflinePlotPlayer {
      *
      * @return UUID
      */
-    @Override public abstract UUID getUUID();
+    @Override @Nonnull public abstract UUID getUUID();
 
     public boolean canTeleport(Location loc) {
         Location current = getLocationFull();
diff --git a/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/util/UUIDHandler.java b/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/util/UUIDHandler.java
index c2aebe971..6696edbd5 100644
--- a/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/util/UUIDHandler.java
+++ b/Core/src/main/java/com/github/intellectualsites/plotsquared/plot/util/UUIDHandler.java
@@ -8,6 +8,7 @@ import com.github.intellectualsites.plotsquared.plot.object.StringWrapper;
 import com.github.intellectualsites.plotsquared.plot.uuid.UUIDWrapper;
 import com.google.common.collect.BiMap;
 
+import javax.annotation.Nonnull;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Map;
@@ -82,10 +83,7 @@ public class UUIDHandler {
         implementation.add(toAdd);
     }
 
-    public static UUID getUUID(PlotPlayer player) {
-        if (implementation == null) {
-            return null;
-        }
+    @Nonnull public static UUID getUUID(PlotPlayer player) {
         return implementation.getUUID(player);
     }
 
diff --git a/Core/src/test/java/com/github/intellectualsites/plotsquared/plot/database/AbstractDBTest.java b/Core/src/test/java/com/github/intellectualsites/plotsquared/plot/database/AbstractDBTest.java
index 1ef04abba..1ef5c92ec 100644
--- a/Core/src/test/java/com/github/intellectualsites/plotsquared/plot/database/AbstractDBTest.java
+++ b/Core/src/test/java/com/github/intellectualsites/plotsquared/plot/database/AbstractDBTest.java
@@ -4,6 +4,7 @@ import com.github.intellectualsites.plotsquared.plot.flag.Flag;
 import com.github.intellectualsites.plotsquared.plot.object.*;
 import com.github.intellectualsites.plotsquared.plot.object.comment.PlotComment;
 
+import javax.annotation.Nonnull;
 import java.util.*;
 
 public class AbstractDBTest implements AbstractDB {
@@ -148,8 +149,8 @@ public class AbstractDBTest implements AbstractDB {
     @Override public void setComment(Plot plot, PlotComment comment) {
     }
 
-    @Override
-    public void getComments(Plot plot, String inbox, RunnableVal<List<PlotComment>> whenDone) {
+    @Override public void getComments(@Nonnull Plot plot, String inbox,
+        RunnableVal<List<PlotComment>> whenDone) {
     }
 
     @Override public void createPlotAndSettings(Plot plot, Runnable whenDone) {