I took a look at the paginate_links()
source code (v3.5.1) and there is this line (#)
$link = str_replace('%_%', 1 == $n ? '' : $format, $base);
that is giving you the empty string for the n=1 page.
With your setup you have $base = "%_%"
and $format = "http://example.com/page/%#%/"
so this becomes:
$link = str_replace('%_%', 1 == $n ? '' : "http://example.com/page/%#%/", "%_%");
where we have 2 cases:
n=1: $link = str_replace('%_%', '', "%_%");
n>1: $link = str_replace('%_%', "http://example.com/page/%#%/", "%_%");
and after the replace:
n=1: $link = '';
n>1: $link = "http://example.com/page/%#%/";
Here is an example of the output from paginate_links()
:
<ul class='page-numbers'>
<li><a class="prev page-numbers" href="http://example.com/page/2/">« Previous</a></li>
<li><a class='page-numbers' href=''>1</a></li>
<li><a class='page-numbers' href='http://example.com/page/2/'>2</a></li>
<li><span class='page-numbers current'>3</span></li>
<li><a class='page-numbers' href='http://example.com/page/4/'>4</a></li>
<li><a class='page-numbers' href='http://example.com/page/5/'>5</a></li>
<li><a class='page-numbers' href='http://example.com/page/6/'>6</a></li>
<li><a class="next page-numbers" href="http://example.com/page/4/">Next »</a></li>
</ul>
If you use instead (#):
'base' => str_replace( $big, '%#%', esc_url( get_pagenum_link( $big ) ) ),
'format' => '?paged=%#%',
you will get a non empty homelink and the the output of paginate_links()
would be something like:
<ul class='page-numbers'>
<li><a class="prev page-numbers" href="http://example.com/page/2/">« Previous</a></li>
<li><a class='page-numbers' href='http://example.com/page/1/'>1</a></li>
<li><a class='page-numbers' href='http://example.com/page/2/'>2</a></li>
<li><span class='page-numbers current'>3</span></li>
<li><a class='page-numbers' href='http://example.com/page/4/'>4</a></li>
<li><a class='page-numbers' href='http://example.com/page/5/'>5</a></li>
<li><a class='page-numbers' href='http://example.com/page/6/'>6</a></li>
<li><a class="next page-numbers" href="http://example.com/page/4/">Next »</a></li>
</ul>