Add documentation for the `allow_empty` param of `glob`.

RELNOTES: None
PiperOrigin-RevId: 293659963
diff --git a/src/main/java/com/google/devtools/build/docgen/templates/be/functions.vm b/src/main/java/com/google/devtools/build/docgen/templates/be/functions.vm
index 123e334..2d19945 100644
--- a/src/main/java/com/google/devtools/build/docgen/templates/be/functions.vm
+++ b/src/main/java/com/google/devtools/build/docgen/templates/be/functions.vm
@@ -301,7 +301,7 @@
 
 <h2 id="glob">glob</h2>
 
-<pre>glob(include, exclude=[], exclude_directories=1)</pre>
+<pre>glob(include, exclude=[], exclude_directories=1, allow_empty=True)</pre>
 
 <p>
 Glob is a helper function that can be used anywhere a list of filenames
@@ -327,6 +327,11 @@
 type directory will be omitted from the results (default 1).
 </p>
 <p>
+If the <code>allow_empty</code> argument is set to <code>False<\code>, the
+<code>glob</code> function will error-out if the result would otherwise be the
+empty list.
+</p>
+<p>
 There are several important limitations and caveats:
 </p>