diff --git a/.github/workflows/phpunit-tests.yml b/.github/workflows/phpunit-tests.yml
index ccd52008928a2..ddcf942346917 100644
--- a/.github/workflows/phpunit-tests.yml
+++ b/.github/workflows/phpunit-tests.yml
@@ -72,7 +72,7 @@ jobs:
       fail-fast: false
       matrix:
         os: [ ubuntu-24.04 ]
-        php: [ '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4' ]
+        php: [ '7.2', '7.3', '7.4', '8.0', '8.1', '8.2', '8.3', '8.4', '8.5' ]
         db-type: [ 'mysql' ]
         db-version: [ '5.7', '8.0', '8.4' ]
         tests-domain: [ 'example.org' ]
diff --git a/src/wp-includes/class-wp-block-bindings-registry.php b/src/wp-includes/class-wp-block-bindings-registry.php
index dc065356c5ce4..519453d22ba92 100644
--- a/src/wp-includes/class-wp-block-bindings-registry.php
+++ b/src/wp-includes/class-wp-block-bindings-registry.php
@@ -249,11 +249,11 @@ public function get_registered( string $source_name ) {
 	 *
 	 * @since 6.5.0
 	 *
-	 * @param string $source_name The name of the source.
+	 * @param string|null $source_name The name of the source.
 	 * @return bool `true` if the block bindings source is registered, `false` otherwise.
 	 */
 	public function is_registered( $source_name ) {
-		return isset( $this->sources[ $source_name ] );
+		return isset( $source_name, $this->sources[ $source_name ] );
 	}
 
 	/**
diff --git a/src/wp-includes/class-wp-block-pattern-categories-registry.php b/src/wp-includes/class-wp-block-pattern-categories-registry.php
index 2d5fbcf2fe10f..05ddce8af0547 100644
--- a/src/wp-includes/class-wp-block-pattern-categories-registry.php
+++ b/src/wp-includes/class-wp-block-pattern-categories-registry.php
@@ -138,11 +138,11 @@ public function get_all_registered( $outside_init_only = false ) {
 	 *
 	 * @since 5.5.0
 	 *
-	 * @param string $category_name Pattern category name including namespace.
+	 * @param string|null $category_name Pattern category name including namespace.
 	 * @return bool True if the pattern category is registered, false otherwise.
 	 */
 	public function is_registered( $category_name ) {
-		return isset( $this->registered_categories[ $category_name ] );
+		return isset( $category_name, $this->registered_categories[ $category_name ] );
 	}
 
 	/**
diff --git a/src/wp-includes/class-wp-block-patterns-registry.php b/src/wp-includes/class-wp-block-patterns-registry.php
index 2afa8a853f1b9..4667979fc72b5 100644
--- a/src/wp-includes/class-wp-block-patterns-registry.php
+++ b/src/wp-includes/class-wp-block-patterns-registry.php
@@ -238,11 +238,11 @@ public function get_all_registered( $outside_init_only = false ) {
 	 *
 	 * @since 5.5.0
 	 *
-	 * @param string $pattern_name Block pattern name including namespace.
+	 * @param string|null $pattern_name Block pattern name including namespace.
 	 * @return bool True if the pattern is registered, false otherwise.
 	 */
 	public function is_registered( $pattern_name ) {
-		return isset( $this->registered_patterns[ $pattern_name ] );
+		return isset( $pattern_name, $this->registered_patterns[ $pattern_name ] );
 	}
 
 	public function __wakeup() {
diff --git a/src/wp-includes/class-wp-block-styles-registry.php b/src/wp-includes/class-wp-block-styles-registry.php
index 8fb5e2eb23820..60c799898580a 100644
--- a/src/wp-includes/class-wp-block-styles-registry.php
+++ b/src/wp-includes/class-wp-block-styles-registry.php
@@ -181,12 +181,12 @@ public function get_registered_styles_for_block( $block_name ) {
 	 *
 	 * @since 5.3.0
 	 *
-	 * @param string $block_name       Block type name including namespace.
-	 * @param string $block_style_name Block style name.
+	 * @param string|null $block_name       Block type name including namespace.
+	 * @param string|null $block_style_name Block style name.
 	 * @return bool True if the block style is registered, false otherwise.
 	 */
 	public function is_registered( $block_name, $block_style_name ) {
-		return isset( $this->registered_block_styles[ $block_name ][ $block_style_name ] );
+		return isset( $block_name, $block_style_name, $this->registered_block_styles[ $block_name ][ $block_style_name ] );
 	}
 
 	/**
diff --git a/src/wp-includes/class-wp-block-templates-registry.php b/src/wp-includes/class-wp-block-templates-registry.php
index 1a1c259dba1dc..966eb1e65bfc7 100644
--- a/src/wp-includes/class-wp-block-templates-registry.php
+++ b/src/wp-includes/class-wp-block-templates-registry.php
@@ -204,11 +204,11 @@ public function get_by_query( $query = array() ) {
 	 *
 	 * @since 6.7.0
 	 *
-	 * @param string $template_name Template name.
+	 * @param string|null $template_name Template name.
 	 * @return bool True if the template is registered, false otherwise.
 	 */
 	public function is_registered( $template_name ) {
-		return isset( $this->registered_templates[ $template_name ] );
+		return isset( $template_name, $this->registered_templates[ $template_name ] );
 	}
 
 	/**
diff --git a/tests/phpunit/tests/block-bindings/wpBlockBindingsRegistry.php b/tests/phpunit/tests/block-bindings/wpBlockBindingsRegistry.php
index 9beebaa2c3108..9ea0933a9c299 100644
--- a/tests/phpunit/tests/block-bindings/wpBlockBindingsRegistry.php
+++ b/tests/phpunit/tests/block-bindings/wpBlockBindingsRegistry.php
@@ -344,4 +344,16 @@ public function test_is_registered_for_known_source() {
 		$result = $this->registry->is_registered( self::$test_source_name );
 		$this->assertTrue( $result );
 	}
+
+	/**
+	 * Should return false when checking registration with a null source name.
+	 *
+	 * @ticket 63957
+	 *
+	 * @covers WP_Block_Bindings_Registry::is_registered
+	 */
+	public function test_is_registered_with_null_source_name() {
+		$result = $this->registry->is_registered( null );
+		$this->assertFalse( $result );
+	}
 }
diff --git a/tests/phpunit/tests/block-pattern/wpBlockPatternCategoriesRegistry.php b/tests/phpunit/tests/block-pattern/wpBlockPatternCategoriesRegistry.php
new file mode 100644
index 0000000000000..8a6700d69db41
--- /dev/null
+++ b/tests/phpunit/tests/block-pattern/wpBlockPatternCategoriesRegistry.php
@@ -0,0 +1,22 @@
+<?php
+/**
+ * Unit tests for WP_Block_Pattern_Categories_Registry::is_registered().
+ *
+ * @package WordPress
+ * @subpackage Blocks
+ * @since 6.9.0
+ *
+ * @group block-patterns
+ * @covers WP_Block_Pattern_Categories_Registry::is_registered
+ */
+
+class Tests_Block_Pattern_WPBlockPatternCategoriesRegistry extends WP_UnitTestCase {
+
+	/**
+	 * @ticket 63957
+	 */
+	public function test_is_registered_with_null_category_name() {
+		$registry = WP_Block_Pattern_Categories_Registry::get_instance();
+		$this->assertFalse( $registry->is_registered( null ) );
+	}
+}
diff --git a/tests/phpunit/tests/block-templates/WpBlockTemplatesRegistry.php b/tests/phpunit/tests/block-templates/WpBlockTemplatesRegistry.php
index a2b1d16eef618..e4675ad210751 100644
--- a/tests/phpunit/tests/block-templates/WpBlockTemplatesRegistry.php
+++ b/tests/phpunit/tests/block-templates/WpBlockTemplatesRegistry.php
@@ -247,6 +247,15 @@ public function test_is_registered() {
 		self::$registry->unregister( $template_name );
 	}
 
+	/**
+	 * @ticket 63957
+	 *
+	 * @covers ::is_registered
+	 */
+	public function test_is_registered_with_null_template_name() {
+		$this->assertFalse( self::$registry->is_registered( null ) );
+	}
+
 	/**
 	 * Tests that unregister() correctly unregisters a registered template.
 	 *
diff --git a/tests/phpunit/tests/blocks/wpBlockPatternsRegistry.php b/tests/phpunit/tests/blocks/wpBlockPatternsRegistry.php
index 378789c231b7f..738d086f4a30e 100644
--- a/tests/phpunit/tests/blocks/wpBlockPatternsRegistry.php
+++ b/tests/phpunit/tests/blocks/wpBlockPatternsRegistry.php
@@ -695,4 +695,11 @@ private function set_registered_patterns_variable_value( $value ) {
 			$property->setAccessible( false );
 		}
 	}
+
+	/**
+	 * @ticket 63957
+	 */
+	public function test_is_registered_with_null_pattern_name() {
+		$this->assertFalse( $this->registry->is_registered( null ) );
+	}
 }
diff --git a/tests/phpunit/tests/blocks/wpBlockStylesRegistry.php b/tests/phpunit/tests/blocks/wpBlockStylesRegistry.php
index f73ba67ba1619..6d3ff4e54a42e 100644
--- a/tests/phpunit/tests/blocks/wpBlockStylesRegistry.php
+++ b/tests/phpunit/tests/blocks/wpBlockStylesRegistry.php
@@ -66,4 +66,36 @@ public function test_register_block_style_with_array_of_block_names() {
 		$this->assertTrue( $this->registry->is_registered( 'core/paragraph', 'plain' ) );
 		$this->assertTrue( $this->registry->is_registered( 'core/group', 'plain' ) );
 	}
+
+	/**
+	 * @ticket 63957
+	 */
+	public function test_is_registered_returns_false_for_null_block_name() {
+		$style_name = 'fancy-style';
+		$this->assertFalse(
+			$this->registry->is_registered( null, $style_name ),
+			'Empty block name should return false.'
+		);
+	}
+
+	/**
+	 * @ticket 63957
+	 */
+	public function test_is_registered_returns_false_for_null_style_name() {
+		$block_name = 'core/paragraph';
+		$this->assertFalse(
+			$this->registry->is_registered( $block_name, null ),
+			'Empty style name should return false.'
+		);
+	}
+
+	/**
+	 * @ticket 63957
+	 */
+	public function test_is_registered_returns_false_for_both_null_params() {
+		$this->assertFalse(
+			$this->registry->is_registered( null, null ),
+			'Both empty block and style name should return false.'
+		);
+	}
 }