Make password lookup treat /dev/null as a special case

I have from time to time a need of random password without
wanting to write them down (one example is mailman list creation,
that requires a password to be given to be sent to the list owner).

But using /dev/null do not return null, but the empty string, which
doesn't generate a password at all and so do not achieve my use case.

test/integration/targets/lookups/tasks/main.yml

@@ -134,6 +134,18 @@
     that:
         - "newpass == newpass2"
 
+- name: verify that we can generate a 1st password without writing it
+  set_fact:
+    newpass: "{{ lookup('password', '/dev/null') }}"
+
+- name: verify that we can generate a 2nd password without writing it
+  set_fact:
+    newpass2: "{{ lookup('password', '/dev/null') }}"
+
+- name: verify lookup password behavior with /dev/null
+  assert:
+    that:
+        - "newpass != newpass2"
 
 # ENV LOOKUP