init: missing widget type should not break awesome

README

@@ -477,7 +477,7 @@ Other
 -----
 Read "awesome" manual pages:
 
-  awesome(1)  awesomerc(5)
+  - awesome(1)  awesomerc(5)
 
 Awesome widgets explained:
 

init.lua

@@ -103,7 +103,7 @@ local function update(widget, reg, disablecache)
 
         data = c.data
     else
-        data = reg.wtype(reg.format, reg.warg)
+        data = reg.wtype and reg.wtype(reg.format, reg.warg)
     end
 
     if type(data) == "table" then
@@ -242,9 +242,11 @@ end
 
 -- {{{ Enable caching of a widget type
 function cache(wtype)
+    if wtype ~= nil then
         if widget_cache[wtype] == nil then
             widget_cache[wtype] = {}
         end
+    end
 end
 -- }}}