fix bug

mybatis-plus/src/main/java/com/baomidou/mybatisplus/mapper/AutoSqlInjector.java

@@ -662,7 +662,7 @@ public class AutoSqlInjector implements ISqlInjector {
 	 */
 	protected String sqlWhereByMap() {
 		StringBuilder where = new StringBuilder();
-		where.append("\n<if test=\"cm!=null\">");
+		where.append("\n<if test=\"cm!=null and !cm.isEmpty\">");
 		where.append("\n WHERE ");
 		where.append("\n<foreach collection=\"cm.keys\" item=\"k\" separator=\"AND\"> ");
 		where.append("\n${k}=#{cm[${k}]}");