Add additional check to copy MySQL behavior

Author: Zodiac1978

tests/WP_SQLite_Translator_Tests.php

@@ -128,6 +128,18 @@ public function testRegexpReplace() {
 
 		$this->assertQuery( "SELECT * FROM _options WHERE REGEXP_REPLACE(option_name, '(-ignore|-remove)', '') = 'test'" );
 		$this->assertCount( 2, $this->engine->get_query_results() );
+
+		$this->assertQuery( 'SELECT REGEXP_REPLACE( null, 'a', 'x') as result' );
+		$results = $this->engine->get_query_results();
+		$this->assertEquals( null, $results[0]->result );
+
+		$this->assertQuery( 'SELECT REGEXP_REPLACE( 'abc', null, 'x') as result' );
+		$results = $this->engine->get_query_results();
+		$this->assertEquals( null, $results[0]->result );
+
+		$this->assertQuery( 'SELECT REGEXP_REPLACE( 'abc', 'a', null) as result' );
+		$results = $this->engine->get_query_results();
+		$this->assertEquals( null, $results[0]->result );
 	}
 
 	public function testInsertDateNow() {

wp-includes/sqlite/class-wp-sqlite-pdo-user-defined-functions.php

@@ -518,6 +518,12 @@ public function regexp_replace( $field, $pattern, $replacement ) {
 		 * be reasonably safe since PHP does not allow null bytes in
 		 * regular expressions anyway.
 		 */
+		
+		/* Return null if one of the required parameter is null */
+		if ( is_null( $field ) || is_null( $pattern ) || is_null( $replacement ) ) {
+			return null;
+		}
+
 		if ( "\x00" === $pattern[0] ) {
 			$pattern = substr( $pattern, 1 );
 			$flags   = '';