problem with helper when used with a text field

I am formatting the value of a text_field.

text_field ... { :value => format_date(@employment_record.hire_date)
...

When a new record does not have a hire_date my helper code gets a
NilClass. My helper code performs checks and only applies formatting
when passed a valid date. When a NilClass is recieved I have tried
returning the NilClass itself, blank strings, test dates, everything
creates a global error.

The helper works fine when not used to set a value on a text_field.

What am I missing?

Thanks.