Within Django views, implement conditions with "vectorized" variables

[Zack-83]

Description / Beschreibung

The Django-language allows defining conditions based on variables's values or on variables being empty.

That does not work for variables which can accept a vector of values.

Expected behaviour / Erwartetes Verhalten

A syntaxe such as {% if var %} or {% if var.is_not.empty %} or {% if var|length > 0 %} should work correctly even if var is allowed to be a collection.

These conditions should be evaluated as False if the variable is empty and as True if the variable has 1,2,3,... components.

Steps to reproduce / Schritte zum Reproduzieren

{% load view_tags %}
{% get_set 'project/dataset/id' as datasets %}
{% get_set 'project/partner/id' as partners %}
{% get_set 'project/funder/id' as funders %}

{% for dataset in datasets %}
	{% get_set_value dataset 'project/dataset/preservation/repository_arrangements' as repository_arrangements %}
	<p><i>Dataset {{ dataset.value }}:</i>
        
	{% if repository_arrangements %}
	    Number of arrangements: {{ repository_arrangements|length }}
	{% else %}
	    Empty List
	{% endif %}
	</p>
	<p>{{ repository_arrangements }}</p>
    
{% endfor %}