Allow empty channel names (but not namespaces).

api/src/main/java/com/velocitypowered/api/proxy/messages/MinecraftChannelIdentifier.java

@@ -12,7 +12,7 @@ import org.checkerframework.checker.nullness.qual.Nullable;
  */
 public final class MinecraftChannelIdentifier implements ChannelIdentifier {
 
-  private static final Pattern VALID_IDENTIFIER_REGEX = Pattern.compile("[a-z0-9\\-_]+");
+  private static final Pattern VALID_IDENTIFIER_REGEX = Pattern.compile("[a-z0-9\\-_]*");
 
   private final String namespace;
   private final String name;
@@ -42,7 +42,7 @@ public final class MinecraftChannelIdentifier implements ChannelIdentifier {
    */
   public static MinecraftChannelIdentifier create(String namespace, String name) {
     Preconditions.checkArgument(!Strings.isNullOrEmpty(namespace), "namespace is null or empty");
-    Preconditions.checkArgument(!Strings.isNullOrEmpty(name), "namespace is null or empty");
+    Preconditions.checkArgument(name != null, "namespace is null or empty");
     Preconditions.checkArgument(VALID_IDENTIFIER_REGEX.matcher(namespace).matches(),
         "namespace is not valid");
     Preconditions

api/src/test/java/com/velocitypowered/api/proxy/messages/MinecraftChannelIdentifierTest.java

@@ -0,0 +1,27 @@
+package com.velocitypowered.api.proxy.messages;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+import org.junit.jupiter.api.Test;
+
+class MinecraftChannelIdentifierTest {
+
+  @Test
+  void createAllowsValidNamespaces() {
+    MinecraftChannelIdentifier.create("minecraft", "brand");
+  }
+
+  @Test
+  void createAllowsEmptyName() {
+    MinecraftChannelIdentifier.create("minecraft", "");
+  }
+
+  @Test
+  void createDisallowsNull() {
+    assertAll(
+        () -> assertThrows(IllegalArgumentException.class, () -> MinecraftChannelIdentifier.create(null, "")),
+        () -> assertThrows(IllegalArgumentException.class, () -> MinecraftChannelIdentifier.create("", "")),
+        () -> assertThrows(IllegalArgumentException.class, () -> MinecraftChannelIdentifier.create("minecraft", null))
+    );
+  }
+}