SPIGOT-2540: Add nullability annotations to entire Bukkit API

By: Darkyenus <darkyenus@gmail.com>

paper-api/src/main/java/org/bukkit/block/Banner.java

@@ -2,6 +2,7 @@ package org.bukkit.block;
 
 import org.bukkit.DyeColor;
 import org.bukkit.block.banner.Pattern;
+import org.jetbrains.annotations.NotNull;
 
 import java.util.List;
 
@@ -15,6 +16,7 @@ public interface Banner extends BlockState {
      *
      * @return the base color
      */
+    @NotNull
     DyeColor getBaseColor();
 
     /**
@@ -24,13 +26,14 @@ public interface Banner extends BlockState {
      *
      * @param color the base color
      */
-    void setBaseColor(DyeColor color);
+    void setBaseColor(@NotNull DyeColor color);
 
     /**
      * Returns a list of patterns on this banner
      *
      * @return the patterns
      */
+    @NotNull
     List<Pattern> getPatterns();
 
     /**
@@ -38,7 +41,7 @@ public interface Banner extends BlockState {
      *
      * @param patterns the new list of patterns
      */
-    void setPatterns(List<Pattern> patterns);
+    void setPatterns(@NotNull List<Pattern> patterns);
 
     /**
      * Adds a new pattern on top of the existing
@@ -46,7 +49,7 @@ public interface Banner extends BlockState {
      *
      * @param pattern the new pattern to add
      */
-    void addPattern(Pattern pattern);
+    void addPattern(@NotNull Pattern pattern);
 
     /**
      * Returns the pattern at the specified index
@@ -54,6 +57,7 @@ public interface Banner extends BlockState {
      * @param i the index
      * @return the pattern
      */
+    @NotNull
     Pattern getPattern(int i);
 
     /**
@@ -62,6 +66,7 @@ public interface Banner extends BlockState {
      * @param i the index
      * @return the removed pattern
      */
+    @NotNull
     Pattern removePattern(int i);
 
     /**
@@ -70,7 +75,7 @@ public interface Banner extends BlockState {
      * @param i       the index
      * @param pattern the new pattern
      */
-    void setPattern(int i, Pattern pattern);
+    void setPattern(int i, @NotNull Pattern pattern);
 
     /**
      * Returns the number of patterns on this