Freemarker function with parameter that can be empty

I created function in Freemarker:

<#function formatDate anyDate>
    <#assign dateFormat = read_from_configuration() />
    <#if anyDate??>
        <#return anyDate?date(dateFormat) />
    <#else >
        <#return '' />
    </#if>
</#function>

I call it like this: ${formatDate(object.someDate)}.

It all works until someDate is null. In that case I get exception:

Error executing macro: f开发者_运维知识库ormatDate
required parameter: anyDate is not specified.

How can I do this? I want the function to work if parameter values is null.

---

Here's what I did, which seems to work in most scenarios:

The default value should be an empty string, and the null-check should be ?has_content.

<#function someFunction optionalParam="" >
    <#if (optionalParam?has_content)>
        <#-- NOT NULL -->
    <#else>
        <#-- NULL -->
    </#if>
</#function>

---

In the end I did it like this:

<#function formatDate anyDate='notSet'>
    <#assign dateFormat = read_from_configuration() />
    <#if anyDate?is_date>
        <#return anyDate?string(dateFormat) />
    <#else >
        <#return '' />
    </#if>
</#function>

---

Freemarker doesn't really handle the null values very well.

I always use the ?has_content on the params to check if there is something in there. The other parameter checkers don't always handle the null value well either so I would suggest something like this:

<#if anyDate?has_content && anyDate?is_date>

just to be sure.