API: Disallow Namespace with null byte character or null level in it

api/src/main/java/org/apache/iceberg/catalog/Namespace.java

@@ -20,6 +20,8 @@
 package org.apache.iceberg.catalog;
 
 import java.util.Arrays;
+import java.util.function.Predicate;
+import java.util.regex.Pattern;
 import org.apache.iceberg.relocated.com.google.common.base.Joiner;
 import org.apache.iceberg.relocated.com.google.common.base.Preconditions;
 
@@ -29,6 +31,8 @@
 public class Namespace {
   private static final Namespace EMPTY_NAMESPACE = new Namespace(new String[] {});
   private static final Joiner DOT = Joiner.on('.');
+  private static final Predicate<String> CONTAINS_NULL_CHARACTER =
+      Pattern.compile("\u0000", Pattern.UNICODE_CHARACTER_CLASS).asPredicate();
 
   public static Namespace empty() {
     return EMPTY_NAMESPACE;
@@ -40,6 +44,13 @@ public static Namespace of(String... levels) {
       return empty();
     }
 
+    for (String level : levels) {
+      Preconditions.checkNotNull(level,
+          "Cannot create a namespace with a null level");
+      Preconditions.checkArgument(!CONTAINS_NULL_CHARACTER.test(level),
+          "Cannot create a namespace with the null-byte character");
+    }
+
     return new Namespace(levels);
   }
 

api/src/test/java/org/apache/iceberg/catalog/TestNamespace.java

@@ -19,6 +19,7 @@
 
 package org.apache.iceberg.catalog;
 
+import org.apache.iceberg.AssertHelpers;
 import org.assertj.core.api.Assertions;
 import org.junit.Test;
 
@@ -44,4 +45,28 @@ public void testNamespace() {
       Assertions.assertThat(namespace.level(i)).isEqualTo(levels[i]);
     }
   }
+
+  @Test
+  public void testWithNullInLevel() {
+    AssertHelpers.assertThrows(
+        "An individual level of a namespace cannot be null",
+        NullPointerException.class,
+        "Cannot create a namespace with a null level",
+        () -> Namespace.of("a", null, "b"));
+  }
+
+  @Test
+  public void testDisallowsNamespaceWithNullByte() {
+    AssertHelpers.assertThrows(
+        "An individual level of a namespace cannot contain the standard null-byte character",
+        IllegalArgumentException.class,
+        "Cannot create a namespace with the null-byte character",
+        () -> Namespace.of("ac", "\u0000c", "b"));
+
+    AssertHelpers.assertThrows(
+        "An individual level of a namespace cannot contain the original ASCII null-byte character",
+        IllegalArgumentException.class,
+        "Cannot create a namespace with the null-byte character",
+        () -> Namespace.of("ac", "c\0", "b"));
+  }
 }