diff --git a/src/wp-includes/functions.php b/src/wp-includes/functions.php
index 62f01fd77a..31f4bee377 100644
--- a/src/wp-includes/functions.php
+++ b/src/wp-includes/functions.php
@@ -4700,9 +4700,9 @@ function absint( $maybeint ) {
  *
  * @param string $function    The function that was called.
  * @param string $version     The version of WordPress that deprecated the function.
- * @param string $replacement Optional. The function that should have been called. Default null.
+ * @param string $replacement Optional. The function that should have been called. Default empty.
  */
-function _deprecated_function( $function, $version, $replacement = null ) {
+function _deprecated_function( $function, $version, $replacement = '' ) {
 
 	/**
 	 * Fires when a deprecated function is called.
@@ -4724,7 +4724,7 @@ function _deprecated_function( $function, $version, $replacement = null ) {
 	 */
 	if ( WP_DEBUG && apply_filters( 'deprecated_function_trigger_error', true ) ) {
 		if ( function_exists( '__' ) ) {
-			if ( ! is_null( $replacement ) ) {
+			if ( $replacement ) {
 				trigger_error(
 					sprintf(
 						/* translators: 1: PHP function name, 2: Version number, 3: Alternative function name. */
@@ -4747,7 +4747,7 @@ function _deprecated_function( $function, $version, $replacement = null ) {
 				);
 			}
 		} else {
-			if ( ! is_null( $replacement ) ) {
+			if ( $replacement ) {
 				trigger_error(
 					sprintf(
 						'%1$s is <strong>deprecated</strong> since version %2$s! Use %3$s instead.',
@@ -4816,7 +4816,7 @@ function _deprecated_constructor( $class, $version, $parent_class = '' ) {
 	 */
 	if ( WP_DEBUG && apply_filters( 'deprecated_constructor_trigger_error', true ) ) {
 		if ( function_exists( '__' ) ) {
-			if ( ! empty( $parent_class ) ) {
+			if ( $parent_class ) {
 				trigger_error(
 					sprintf(
 						/* translators: 1: PHP class name, 2: PHP parent class name, 3: Version number, 4: __construct() method. */
@@ -4841,7 +4841,7 @@ function _deprecated_constructor( $class, $version, $parent_class = '' ) {
 				);
 			}
 		} else {
-			if ( ! empty( $parent_class ) ) {
+			if ( $parent_class ) {
 				trigger_error(
 					sprintf(
 						'The called constructor method for %1$s in %2$s is <strong>deprecated</strong> since version %3$s! Use %4$s instead.',
@@ -4886,10 +4886,10 @@ function _deprecated_constructor( $class, $version, $parent_class = '' ) {
  * @param string $file        The file that was included.
  * @param string $version     The version of WordPress that deprecated the file.
  * @param string $replacement Optional. The file that should have been included based on ABSPATH.
- *                            Default null.
+ *                            Default empty.
  * @param string $message     Optional. A message regarding the change. Default empty.
  */
-function _deprecated_file( $file, $version, $replacement = null, $message = '' ) {
+function _deprecated_file( $file, $version, $replacement = '', $message = '' ) {
 
 	/**
 	 * Fires when a deprecated file is called.
@@ -4914,7 +4914,7 @@ function _deprecated_file( $file, $version, $replacement = null, $message = '' )
 		$message = empty( $message ) ? '' : ' ' . $message;
 
 		if ( function_exists( '__' ) ) {
-			if ( ! is_null( $replacement ) ) {
+			if ( $replacement ) {
 				trigger_error(
 					sprintf(
 						/* translators: 1: PHP file name, 2: Version number, 3: Alternative file name. */
@@ -4937,7 +4937,7 @@ function _deprecated_file( $file, $version, $replacement = null, $message = '' )
 				);
 			}
 		} else {
-			if ( ! is_null( $replacement ) ) {
+			if ( $replacement ) {
 				trigger_error(
 					sprintf(
 						'%1$s is <strong>deprecated</strong> since version %2$s! Use %3$s instead.',
@@ -4984,9 +4984,9 @@ function _deprecated_file( $file, $version, $replacement = null, $message = '' )
  *
  * @param string $function The function that was called.
  * @param string $version  The version of WordPress that deprecated the argument used.
- * @param string $message  Optional. A message regarding the change. Default null.
+ * @param string $message  Optional. A message regarding the change. Default empty.
  */
-function _deprecated_argument( $function, $version, $message = null ) {
+function _deprecated_argument( $function, $version, $message = '' ) {
 
 	/**
 	 * Fires when a deprecated argument is called.
@@ -5008,7 +5008,7 @@ function _deprecated_argument( $function, $version, $message = null ) {
 	 */
 	if ( WP_DEBUG && apply_filters( 'deprecated_argument_trigger_error', true ) ) {
 		if ( function_exists( '__' ) ) {
-			if ( ! is_null( $message ) ) {
+			if ( $message ) {
 				trigger_error(
 					sprintf(
 						/* translators: 1: PHP function name, 2: Version number, 3: Optional message regarding the change. */
@@ -5031,7 +5031,7 @@ function _deprecated_argument( $function, $version, $message = null ) {
 				);
 			}
 		} else {
-			if ( ! is_null( $message ) ) {
+			if ( $message ) {
 				trigger_error(
 					sprintf(
 						'%1$s was called with an argument that is <strong>deprecated</strong> since version %2$s! %3$s',
@@ -5072,10 +5072,10 @@ function _deprecated_argument( $function, $version, $message = null ) {
  *
  * @param string $hook        The hook that was used.
  * @param string $version     The version of WordPress that deprecated the hook.
- * @param string $replacement Optional. The hook that should have been used. Default null.
- * @param string $message     Optional. A message regarding the change. Default null.
+ * @param string $replacement Optional. The hook that should have been used. Default empty.
+ * @param string $message     Optional. A message regarding the change. Default empty.
  */
-function _deprecated_hook( $hook, $version, $replacement = null, $message = null ) {
+function _deprecated_hook( $hook, $version, $replacement = '', $message = '' ) {
 	/**
 	 * Fires when a deprecated hook is called.
 	 *
@@ -5099,7 +5099,7 @@ function _deprecated_hook( $hook, $version, $replacement = null, $message = null
 	if ( WP_DEBUG && apply_filters( 'deprecated_hook_trigger_error', true ) ) {
 		$message = empty( $message ) ? '' : ' ' . $message;
 
-		if ( ! is_null( $replacement ) ) {
+		if ( $replacement ) {
 			trigger_error(
 				sprintf(
 					/* translators: 1: WordPress hook name, 2: Version number, 3: Alternative hook name. */
@@ -5166,9 +5166,7 @@ function _doing_it_wrong( $function, $message, $version ) {
 	 */
 	if ( WP_DEBUG && apply_filters( 'doing_it_wrong_trigger_error', true, $function, $message, $version ) ) {
 		if ( function_exists( '__' ) ) {
-			if ( is_null( $version ) ) {
-				$version = '';
-			} else {
+			if ( $version ) {
 				/* translators: %s: Version number. */
 				$version = sprintf( __( '(This message was added in version %s.)' ), $version );
 			}
@@ -5190,9 +5188,7 @@ function _doing_it_wrong( $function, $message, $version ) {
 				E_USER_NOTICE
 			);
 		} else {
-			if ( is_null( $version ) ) {
-				$version = '';
-			} else {
+			if ( $version ) {
 				$version = sprintf( '(This message was added in version %s.)', $version );
 			}
 
diff --git a/src/wp-includes/plugin.php b/src/wp-includes/plugin.php
index 25c60a5813..6ba09d2b9a 100644
--- a/src/wp-includes/plugin.php
+++ b/src/wp-includes/plugin.php
@@ -620,10 +620,10 @@ function remove_all_actions( $tag, $priority = false ) {
  * @param string $tag         The name of the filter hook.
  * @param array  $args        Array of additional function arguments to be passed to apply_filters().
  * @param string $version     The version of WordPress that deprecated the hook.
- * @param string $replacement Optional. The hook that should have been used. Default null.
- * @param string $message     Optional. A message regarding the change. Default null.
+ * @param string $replacement Optional. The hook that should have been used. Default empty.
+ * @param string $message     Optional. A message regarding the change. Default empty.
  */
-function apply_filters_deprecated( $tag, $args, $version, $replacement = null, $message = null ) {
+function apply_filters_deprecated( $tag, $args, $version, $replacement = '', $message = '' ) {
 	if ( ! has_filter( $tag ) ) {
 		return $args[0];
 	}
@@ -647,10 +647,10 @@ function apply_filters_deprecated( $tag, $args, $version, $replacement = null, $
  * @param string $tag         The name of the action hook.
  * @param array  $args        Array of additional function arguments to be passed to do_action().
  * @param string $version     The version of WordPress that deprecated the hook.
- * @param string $replacement Optional. The hook that should have been used. Default null.
- * @param string $message     Optional. A message regarding the change. Default null.
+ * @param string $replacement Optional. The hook that should have been used. Default empty.
+ * @param string $message     Optional. A message regarding the change. Default empty.
  */
-function do_action_deprecated( $tag, $args, $version, $replacement = null, $message = null ) {
+function do_action_deprecated( $tag, $args, $version, $replacement = '', $message = '' ) {
 	if ( ! has_action( $tag ) ) {
 		return;
 	}