Filter empty database parameters to prevent MySQL command failures

features/db-check.feature

@@ -155,3 +155,31 @@ Feature: Check the database
     When I try `wp db check --no-defaults --debug`
     Then STDERR should match #Debug \(db\): Running shell command: /usr/bin/env (mysqlcheck|mariadb-check) --no-defaults %s#
 
+  Scenario: Empty DB credentials should not cause empty parameter errors
+    Given a WP install
+    And a wp-config.php file:
+      """
+      <?php
+      define( 'DB_NAME', 'wp_cli_test' );
+      define( 'DB_USER', 'wp_cli_test' );
+      define( 'DB_PASSWORD', 'password1' );
+      define( 'DB_HOST', '' );
+      define( 'DB_CHARSET', 'utf8' );
+      $table_prefix = 'wp_';
+      require_once ABSPATH . 'wp-settings.php';
+      """
+
+    When I try `wp db check --debug`
+    Then STDERR should contain:
+      """
+      Debug (db): Final MySQL command:
+      """
+    And STDERR should not contain:
+      """
+      --host=''
+      """
+    And STDERR should not contain:
+      """
+      --host=
+      """
+

src/DB_Command.php

@@ -1853,6 +1853,29 @@ private static function run( $cmd, $assoc_args = [], $send_to_shell = true, $int
 
 		$final_args = array_merge( $required, $assoc_args );
 
+		// Filter out empty string values to avoid passing empty parameters to MySQL commands
+		// which can cause errors like "Character set '' is not a compiled character set".
+		// However, keep empty strings for credential options like 'user' and 'pass' so that
+		// an explicitly empty value is not silently converted into an omitted parameter.
+		$final_args = array_filter(
+			$final_args,
+			static function ( $value, $key ) {
+				// Always drop null values.
+				if ( null === $value ) {
+					return false;
+				}
+
+				// Preserve explicitly empty credential arguments.
+				if ( '' === $value && in_array( $key, [ 'user', 'pass' ], true ) ) {
+					return true;
+				}
+
+				// For all other options, filter out empty strings.
+				return '' !== $value;
+			},
+			ARRAY_FILTER_USE_BOTH
+		);
+
 		// Adapt ordering of arguments.
 		uksort(
 			$final_args,