diff --git a/wp-includes/bookmark.php b/wp-includes/bookmark.php
index b0de276df4..32499541d4 100644
--- a/wp-includes/bookmark.php
+++ b/wp-includes/bookmark.php
@@ -171,13 +171,13 @@ function get_bookmarks( $args = '' ) {
 		$r['exclude']       = '';  //ignore exclude, category, and category_name params if using include
 		$r['category']      = '';
 		$r['category_name'] = '';
-		$inclinks           = preg_split( '/[\s,]+/', $r['include'] );
+		$inclinks           = wp_parse_id_list( $r['include'] );
 		if ( count( $inclinks ) ) {
 			foreach ( $inclinks as $inclink ) {
 				if ( empty( $inclusions ) ) {
-					$inclusions = ' AND ( link_id = ' . intval( $inclink ) . ' ';
+					$inclusions = ' AND ( link_id = ' . $inclink . ' ';
 				} else {
-					$inclusions .= ' OR link_id = ' . intval( $inclink ) . ' ';
+					$inclusions .= ' OR link_id = ' . $inclink . ' ';
 				}
 			}
 		}
@@ -188,13 +188,13 @@ function get_bookmarks( $args = '' ) {
 
 	$exclusions = '';
 	if ( ! empty( $r['exclude'] ) ) {
-		$exlinks = preg_split( '/[\s,]+/', $r['exclude'] );
+		$exlinks = wp_parse_id_list( $r['exclude'] );
 		if ( count( $exlinks ) ) {
 			foreach ( $exlinks as $exlink ) {
 				if ( empty( $exclusions ) ) {
-					$exclusions = ' AND ( link_id <> ' . intval( $exlink ) . ' ';
+					$exclusions = ' AND ( link_id <> ' . $exlink . ' ';
 				} else {
-					$exclusions .= ' AND link_id <> ' . intval( $exlink ) . ' ';
+					$exclusions .= ' AND link_id <> ' . $exlink . ' ';
 				}
 			}
 		}
@@ -223,13 +223,13 @@ function get_bookmarks( $args = '' ) {
 	$category_query = '';
 	$join           = '';
 	if ( ! empty( $r['category'] ) ) {
-		$incategories = preg_split( '/[\s,]+/', $r['category'] );
+		$incategories = wp_parse_id_list( $r['category'] );
 		if ( count( $incategories ) ) {
 			foreach ( $incategories as $incat ) {
 				if ( empty( $category_query ) ) {
-					$category_query = ' AND ( tt.term_id = ' . intval( $incat ) . ' ';
+					$category_query = ' AND ( tt.term_id = ' . $incat . ' ';
 				} else {
-					$category_query .= ' OR tt.term_id = ' . intval( $incat ) . ' ';
+					$category_query .= ' OR tt.term_id = ' . $incat . ' ';
 				}
 			}
 		}
diff --git a/wp-includes/class-wp-comment-query.php b/wp-includes/class-wp-comment-query.php
index af05326915..95ab3a6b35 100644
--- a/wp-includes/class-wp-comment-query.php
+++ b/wp-includes/class-wp-comment-query.php
@@ -482,9 +482,11 @@ class WP_Comment_Query {
 
 		// 'status' accepts an array or a comma-separated string.
 		$status_clauses = array();
-		$statuses       = $this->query_vars['status'];
-		if ( ! is_array( $statuses ) ) {
-			$statuses = preg_split( '/[\s,]+/', $statuses );
+		$statuses       = wp_parse_list( $this->query_vars['status'] );
+
+		// Empty 'status' should be interpreted as 'all'.
+		if ( empty( $statuses ) ) {
+			$statuses = array( 'all' );
 		}
 
 		// 'any' overrides other statuses.
@@ -517,14 +519,10 @@ class WP_Comment_Query {
 
 		// User IDs or emails whose unapproved comments are included, regardless of $status.
 		if ( ! empty( $this->query_vars['include_unapproved'] ) ) {
-			$include_unapproved = $this->query_vars['include_unapproved'];
+			$include_unapproved = wp_parse_list( $this->query_vars['include_unapproved'] );
 
-			// Accepts arrays or comma-separated strings.
-			if ( ! is_array( $include_unapproved ) ) {
-				$include_unapproved = preg_split( '/[\s,]+/', $include_unapproved );
-			}
-
-			$unapproved_ids = $unapproved_emails = array();
+			$unapproved_ids    = array();
+			$unapproved_emails = array();
 			foreach ( $include_unapproved as $unapproved_identifier ) {
 				// Numeric values are assumed to be user ids.
 				if ( is_numeric( $unapproved_identifier ) ) {
diff --git a/wp-includes/functions.php b/wp-includes/functions.php
index 39de1470e2..c790f3df39 100644
--- a/wp-includes/functions.php
+++ b/wp-includes/functions.php
@@ -3822,6 +3822,22 @@ function wp_parse_args( $args, $defaults = '' ) {
 	return $r;
 }
 
+/**
+ * Cleans up an array, comma- or space-separated list of scalar values.
+ *
+ * @since 5.1.0
+ *
+ * @param array|string $list List of values.
+ * @return array Sanitized array of values.
+ */
+function wp_parse_list( $list ) {
+	if ( ! is_array( $list ) ) {
+		return preg_split( '/[\s,]+/', $list, -1, PREG_SPLIT_NO_EMPTY );
+	}
+
+	return $list;
+}
+
 /**
  * Clean up an array, comma- or space-separated list of IDs.
  *
@@ -3831,9 +3847,7 @@ function wp_parse_args( $args, $defaults = '' ) {
  * @return array Sanitized array of IDs.
  */
 function wp_parse_id_list( $list ) {
-	if ( ! is_array( $list ) ) {
-		$list = preg_split( '/[\s,]+/', $list );
-	}
+	$list = wp_parse_list( $list );
 
 	return array_unique( array_map( 'absint', $list ) );
 }
@@ -3847,15 +3861,9 @@ function wp_parse_id_list( $list ) {
  * @return array Sanitized array of slugs.
  */
 function wp_parse_slug_list( $list ) {
-	if ( ! is_array( $list ) ) {
-		$list = preg_split( '/[\s,]+/', $list );
-	}
+	$list = wp_parse_list( $list );
 
-	foreach ( $list as $key => $value ) {
-		$list[ $key ] = sanitize_title( $value );
-	}
-
-	return array_unique( $list );
+	return array_unique( array_map( 'sanitize_title', $list ) );
 }
 
 /**
diff --git a/wp-includes/post.php b/wp-includes/post.php
index f3696341da..565c243bbc 100644
--- a/wp-includes/post.php
+++ b/wp-includes/post.php
@@ -5088,7 +5088,7 @@ function get_pages( $args = array() ) {
 
 	$author_query = '';
 	if ( ! empty( $r['authors'] ) ) {
-		$post_authors = preg_split( '/[\s,]+/', $r['authors'] );
+		$post_authors = wp_parse_list( $r['authors'] );
 
 		if ( ! empty( $post_authors ) ) {
 			foreach ( $post_authors as $post_author ) {
diff --git a/wp-includes/rest-api.php b/wp-includes/rest-api.php
index 1c8bb4620e..e0807e7696 100644
--- a/wp-includes/rest-api.php
+++ b/wp-includes/rest-api.php
@@ -679,7 +679,7 @@ function rest_filter_response_fields( $response, $server, $request ) {
 
 	$data = $response->get_data();
 
-	$fields = is_array( $request['_fields'] ) ? $request['_fields'] : preg_split( '/[\s,]+/', $request['_fields'] );
+	$fields = wp_parse_list( $request['_fields'] );
 
 	if ( 0 === count( $fields ) ) {
 		return $response;
@@ -1109,8 +1109,8 @@ function rest_get_avatar_sizes() {
  */
 function rest_validate_value_from_schema( $value, $args, $param = '' ) {
 	if ( 'array' === $args['type'] ) {
-		if ( ! is_array( $value ) ) {
-			$value = preg_split( '/[\s,]+/', $value );
+		if ( ! is_null( $value ) ) {
+			$value = wp_parse_list( $value );
 		}
 		if ( ! wp_is_numeric_array( $value ) ) {
 			/* translators: 1: parameter, 2: type name */
@@ -1253,9 +1253,7 @@ function rest_sanitize_value_from_schema( $value, $args ) {
 		if ( empty( $args['items'] ) ) {
 			return (array) $value;
 		}
-		if ( ! is_array( $value ) ) {
-			$value = preg_split( '/[\s,]+/', $value );
-		}
+		$value = wp_parse_list( $value );
 		foreach ( $value as $index => $v ) {
 			$value[ $index ] = rest_sanitize_value_from_schema( $v, $args['items'] );
 		}
diff --git a/wp-includes/rest-api/endpoints/class-wp-rest-controller.php b/wp-includes/rest-api/endpoints/class-wp-rest-controller.php
index 6dc971517d..d610504692 100644
--- a/wp-includes/rest-api/endpoints/class-wp-rest-controller.php
+++ b/wp-includes/rest-api/endpoints/class-wp-rest-controller.php
@@ -532,7 +532,7 @@ abstract class WP_REST_Controller {
 		if ( ! isset( $request['_fields'] ) ) {
 			return $fields;
 		}
-		$requested_fields = is_array( $request['_fields'] ) ? $request['_fields'] : preg_split( '/[\s,]+/', $request['_fields'] );
+		$requested_fields = wp_parse_list( $request['_fields'] );
 		if ( 0 === count( $requested_fields ) ) {
 			return $fields;
 		}
diff --git a/wp-includes/version.php b/wp-includes/version.php
index b225cb356b..5d8cbfe002 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-alpha-44545';
+$wp_version = '5.1-alpha-44546';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.