diff --git a/src/wp-includes/class-wp-theme-json.php b/src/wp-includes/class-wp-theme-json.php
index 749ee90c0c..4f5627a790 100644
--- a/src/wp-includes/class-wp-theme-json.php
+++ b/src/wp-includes/class-wp-theme-json.php
@@ -1709,7 +1709,12 @@ class WP_Theme_JSON {
 	 * @return string|array Style property value.
 	 */
 	protected static function get_property_value( $styles, $path, $theme_json = null ) {
-		$value = _wp_array_get( $styles, $path );
+		$value = _wp_array_get( $styles, $path, '' );
+
+		if ( '' === $value || null === $value ) {
+			// No need to process the value further.
+			return '';
+		}
 
 		/*
 		 * This converts references to a path to the value at that path
diff --git a/tests/phpunit/tests/theme/wpThemeJson.php b/tests/phpunit/tests/theme/wpThemeJson.php
index 4cc81c98b2..1eb8bb4f6e 100644
--- a/tests/phpunit/tests/theme/wpThemeJson.php
+++ b/tests/phpunit/tests/theme/wpThemeJson.php
@@ -2996,6 +2996,54 @@ class Tests_Theme_wpThemeJson extends WP_UnitTestCase {
 		$this->assertSame( $expected, $theme_json->get_stylesheet() );
 	}
 
+	/**
+	 * Tests that get_property_value() static method returns an empty string
+	 * if the path is invalid or the value is null.
+	 *
+	 * Also, tests that PHP 8.1 "passing null to non-nullable" deprecation notice
+	 * is not thrown when passing the value to strncmp() in the method.
+	 *
+	 * The notice that we should not see:
+	 * `Deprecated: strncmp(): Passing null to parameter #1 ($string1) of type string is deprecated`.
+	 *
+	 * @dataProvider data_get_property_value_should_return_string_for_invalid_paths_or_null_values
+	 *
+	 * @ticket 56620
+	 *
+	 * @covers WP_Theme_JSON::get_property_value
+	 *
+	 * @param array $styles An array with style definitions.
+	 * @param array $path   Path to the desired properties.
+	 *
+	 */
+	public function test_get_property_value_should_return_string_for_invalid_paths_or_null_values( $styles, $path ) {
+		$reflection_class = new ReflectionClass( WP_Theme_JSON::class );
+
+		$get_property_value_method = $reflection_class->getMethod( 'get_property_value' );
+		$get_property_value_method->setAccessible( true );
+		$result = $get_property_value_method->invoke( null, $styles, $path );
+
+		$this->assertSame( '', $result );
+	}
+
+	/**
+	 * Data provider for test_get_property_value_should_return_string_for_invalid_paths_or_null_values().
+	 *
+	 * @return array
+	 */
+	public function data_get_property_value_should_return_string_for_invalid_paths_or_null_values() {
+		return array(
+			'empty string' => array(
+				'styles' => array(),
+				'path'   => array( 'non_existent_path' ),
+			),
+			'null'         => array(
+				'styles' => array( 'some_null_value' => null ),
+				'path'   => array( 'some_null_value' ),
+			),
+		);
+	}
+
 	/**
 	 * Testing that dynamic properties in theme.json that refer to other dynamic properties in a loop
 	 * should be left untouched.
@@ -3084,7 +3132,6 @@ class Tests_Theme_wpThemeJson extends WP_UnitTestCase {
 		$this->assertSame( $expected, $theme_json->get_stylesheet() );
 	}
 
-
 	/**
 	 * @dataProvider data_get_layout_definitions
 	 *