fix(gson): Better handle null input

This still isn't perfect, but we shouldn't break the contract and return `null` when we parse any other primitive string as a text component.

Author: kezz

text-serializer-commons/src/main/java/net/kyori/adventure/text/serializer/commons/ComponentTreeConstants.java

@@ -93,6 +93,7 @@ public final class ComponentTreeConstants {
   @ApiStatus.Obsolete
   public static final String SHOW_ITEM_TAG = "tag";
   public static final String SHOW_ITEM_COMPONENTS = "components";
+  public static final String NULL = "null";
 
   private ComponentTreeConstants() {
     throw new IllegalStateException("Cannot instantiate");

text-serializer-gson/src/main/java/net/kyori/adventure/text/serializer/gson/GsonComponentSerializerImpl.java

@@ -36,6 +36,7 @@
 import org.jspecify.annotations.Nullable;
 
 import static java.util.Objects.requireNonNull;
+import static net.kyori.adventure.text.serializer.commons.ComponentTreeConstants.NULL;
 
 final class GsonComponentSerializerImpl implements GsonComponentSerializer {
   private static final Optional<Provider> SERVICE = Services.service(Provider.class);
@@ -85,6 +86,7 @@ public UnaryOperator<GsonBuilder> populator() {
 
   @Override
   public Component deserialize(final String string) {
+    if (NULL.equals(string)) return Component.text(NULL);
     return this.serializer().fromJson(string, Component.class);
   }
 

text-serializer-json/src/testFixtures/java/net/kyori/adventure/text/serializer/json/JSONComponentSerializerTest.java

@@ -29,14 +29,16 @@
 import net.kyori.adventure.text.serializer.commons.ComponentTreeConstants;
 import org.junit.jupiter.api.Test;
 
+import static net.kyori.adventure.text.serializer.commons.ComponentTreeConstants.NULL;
 import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
 final class JSONComponentSerializerTest extends SerializerTest {
   @Test
   void testDeserializeNull() {
-    assertNull(JSONComponentSerializer.json().deserialize("null"));
+    assertNotNull(JSONComponentSerializer.json().deserialize(NULL));
+    assertEquals(Component.text(NULL), JSONComponentSerializer.json().deserialize(NULL));
   }
 
   @Test