freemarker test for list and iterate it - templates

Question

I have a data element that can either be a Map or a List of Maps.
Here are two simplified data examples (expressed as JSON for readability)
1) Maps
{
"lom:general": {
"lom:title": {"lom:string": {
"language": "fr",
"content": "Premiers Pas avec un Progiciel de Gestion Intégré"
}},
"lom:language": "fr"
},
"lom:technical": {"lom:location": "http://hub11.ecolearning.eu/course/progiciel-metiers-pgi/"}
}
2) List of Maps
{
"lom:general": {
"lom:title": {"lom:string": [
{
"language": "fr",
"content": "DIY Education aux médias et à l'information - 3ed"
},
{
"language": "en",
"content": "DIY Media and Information Literacy - 3ed"
}
]},
"lom:language": [
"fr",
"en"
]
},
"lom:technical": {"lom:location": "http://hub5.ecolearning.eu/course/diy-do-it-yourself/"}
}
I want to check the type of element lom:general.lom:title.lom:string and iterate it if it is a list.
I have tried the following:
<title>
<#assign titles = lom\:general.lom\:title.lom\:string>
<#if titles?is_enumerable>
<#list titles as title>
<string language="${title.language}">${title.content}</string>
</#list>
<#else>
<string language="${titles.language}">${titles.content}</string>
</#if>
</title>
The template works as expected with the first data example. However, the second data example raises a StackOverflowError
java.lang.StackOverflowError
at sun.reflect.misc.ReflectUtil.checkPackageAccess(ReflectUtil.java:188)
at sun.reflect.misc.ReflectUtil.checkPackageAccess(ReflectUtil.java:164)
at sun.reflect.generics.reflectiveObjects.TypeVariableImpl.getGenericDeclaration(TypeVariableImpl.java:164)
at sun.reflect.generics.reflectiveObjects.TypeVariableImpl.equals(TypeVariableImpl.java:189)
at com.sun.beans.TypeResolver.resolve(TypeResolver.java:190)
at com.sun.beans.TypeResolver.resolve(TypeResolver.java:201)
Where the last line is repeated dozens of times