Test for empty field?
The answer depends on the field type.

Assets, Categories, Checkboxes, Dropdown, Entries, Matrix, Multi-select, Radio Buttons, Tags, and Users fields each will each appear to be non-empty, even if they don’t have a user-submitted value, because in each case, entry.myFieldHandle will still return something:


an ElementCriteriaModel object for Assets, Categories, Entries, Matrix, Tags, and Users fields
a MultiOptionsFieldData object for Checkboxes and Multi-select fields
a SingleOptionFieldData object for Dropdown and Radio Buttons fields


So for each of those field types, you will need to use the |length filter to determine if there is an actual value.

{% if not entry.myCheckboxesField|length %}


Also worth noting for Assets, Categories, Entries, Matrix, Tags, and Users fields: ElementCriteriaModel objects also have a total() function which can be used to speed up your template if all you need to know is whether any elements were selected, and you won’t be actually looping through them further down in the template. (|length actually fetches the elements first, and then returns the count of the results, but stores those elements internally in case they are going to be looped through later on. .total() runs a separate, much less expensive DB query, but the results won’t be cached internally for later use.)

{% if not entry.myCategoriesField.total() %}


Color, Date/Time, Lightswitch, Number, Plain Text, Rich Text, and Table fields will each return an empty value (null, an empty string/array, etc.) when there is no value, so each of those field types are safe to use with the is empty test:

{% if entry.myTextField is empty %}


This would also work:

{% if not entry.myTextField %}


In all cases, the |length filter will work as expected, so if you don’t want to remember this stuff, just use that.