Bug#5081: UCS2 fields are filled with '0x2020' after extending field length

mysql-test/r/ctype_ucs.result

@@ -470,3 +470,13 @@ select s1 from t1 where s1 > 'a' order by s1;
 s1
 b
 c
+drop table t1;
+create table t1(a char(1)) default charset = ucs2;
+insert into t1 values ('a'),('b'),('c');
+alter table t1 modify a char(5);
+select a, hex(a) from t1;
+a	hex(a)
+a	0061
+b	0062
+c	0063
+drop table t1;

mysql-test/t/ctype_ucs.test

@@ -303,4 +303,15 @@ DROP TABLE t1;
 create table t1 (s1 char character set `ucs2` collate `ucs2_czech_ci`);
 insert into t1 values ('0'),('1'),('2'),('a'),('b'),('c');
 select s1 from t1 where s1 > 'a' order by s1;
+drop table t1;
+
+#
+# Bug #5081 : UCS2 fields are filled with '0x2020'
+# after extending field length
+#
+create table t1(a char(1)) default charset = ucs2;
+insert into t1 values ('a'),('b'),('c');
+alter table t1 modify a char(5);
+select a, hex(a) from t1;
+drop table t1;
 

sql/field_conv.cc

@@ -340,8 +340,10 @@ static void do_cut_string(Copy_field *copy)
 
 static void do_expand_string(Copy_field *copy)
 {
+  CHARSET_INFO *cs= copy->from_field->charset();
   memcpy(copy->to_ptr,copy->from_ptr,copy->from_length);
-  bfill(copy->to_ptr+copy->from_length,copy->to_length-copy->from_length,' ');
+  cs->cset->fill(cs, copy->to_ptr+copy->from_length,
+                     copy->to_length-copy->from_length, ' ');
 }
 
 static void do_varstring(Copy_field *copy)