diff --git a/chandler/procedural/mimes.php b/chandler/procedural/mimes.php
index 645b393..e2450e4 100644
--- a/chandler/procedural/mimes.php
+++ b/chandler/procedural/mimes.php
@@ -1,4 +1,5 @@
 <?php declare(strict_types=1);
+
 function system_extension_mime_types(): array
 {
     # Returns the system MIME type mapping of extensions to MIME types, as defined in /etc/mime.types.
@@ -19,7 +20,7 @@ function system_extension_mime_types(): array
     return $out;
 }
 
-function system_extension_mime_type(string $file): string
+function system_extension_mime_type(string $file): ?string
 {
     # Returns the system MIME type (as defined in /etc/mime.types) for the filename specified.
     #
@@ -60,7 +61,7 @@ function system_mime_type_extensions(): array
     return $out;
 }
 
-function system_mime_type_extension(string $type): string
+function system_mime_type_extension(string $type): ?string
 {
     # Returns the canonical file extension for the MIME type specified, as defined in /etc/mime.types (considering the first
     # extension listed to be canonical).
@@ -70,4 +71,4 @@ function system_mime_type_extension(string $type): string
     if(!isset($exts))
         $exts = system_mime_type_extensions();
     return isset($exts[$type]) ? $exts[$type] : null;
-}
\ No newline at end of file
+}