svn: Item is not readable

My svn server had a simple authentication and authorization like below.

svnserve.conf

[general]
anon-access = read
auth-access = write
password-db = passwd
authz-db = authz
realm = My First Repository

authz

[groups]
admin = shylu

[/]
@admin = rw

With this configuration svn log command always failed with a "svn: Item is not readable" error.

Problem is, even though anon-access has read permission in svnserve.conf, authz file must explicitly specify read permission to everyone like below.

new authz

[groups]
admin = shylu

[/]
* = r
@admin = rw