Merge pull request #320 from freyes/fix-pip_constraints_url

Get the constraints file only when holds a valid value

roles/handle-constraints-url/tasks/main.yaml

@@ -3,20 +3,24 @@
     path: /home/ubuntu/
     prefix: "constraints."
     suffix: ".txt"
-  when: pip_constraints_url is defined
   register: constraints_file
 
 - name: GET the constraints file
   get_url:
     url: "{{ pip_constraints_url }}"
     dest: "{{ constraints_file.path }}"
     mode: 0444
-  when: constraints_file is defined and pip_constraints_url is defined
+  when: constraints_file is defined and pip_constraints_url is defined and pip_constraints_url != null and pip_constraints_url|length > 0
+
+- name: Get stat of temporary constraints file
+  ansible.builtin.stat:
+    path: "{{ constraints_file.path }}"
+  register: constraints_stat
 
 - name: Record file location
   set_fact:
     tox_constraints_env:
       TOX_CONSTRAINTS_FILE: "{{ constraints_file.path }}"
       # Backward compatibility, to be removed
       UPPER_CONSTRAINTS_FILE: "{{ constraints_file.path }}"
-  when: constraints_file is defined and pip_constraints_url is defined
+  when: constraints_stat.size > 0