FreeMarker

i want to iterate through a hash checking for keys and variations of keys.
for example:

<#list myhash?keys as key>
<#if myhash[key] == 'foo'>
do something
<#elseif myhash[key + 'variation'] == 'bar'>
do something else
</#if>
</#list>

if key + 'variation' doesn't exist in myhash, then SimpleHash will do a put
(SimpleHash line 204), which will cause a ConcurrentModificationException
on the next iteration because the hash has been modified.

the reason for the put seems to be to cache the value wrapped in a
TemplateModel. i'm sure this is a good thing for performance reasons, but
it obviously has its side effects.

the solution is to not add a new entry to the hash. if you are just
replacing the value for a particular key with a new value, then you won't
trigger a ConcurrentModificationException. but if the key isn't in the
hash, then you shouldn't add it.

so after line 202, add this:

if (result == null) return tm;