[commons/system] more fixes related to some backend commands hanging

CHANGELOG.md

@@ -6,6 +6,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ## [0.9.21] 2021
 ### Fixes
+- General
+  - more fixes related to some backend commands hanging
 - Flatpak
   - not displaying update components not associated with installed packages 
   - not displaying the updates size for Flatpak 1.2

bauh/commons/system.py

@@ -243,12 +243,10 @@ def new_subprocess(cmd: List[str], cwd: str = '.', shell: bool = False, stdin =
         "stderr": PIPE,
         "cwd": cwd,
         "shell": shell,
-        "env": gen_env(global_interpreter, lang, extra_paths)
+        "env": gen_env(global_interpreter, lang, extra_paths),
+        "stdin": stdin if stdin else subprocess.DEVNULL
     }
 
-    if input:
-        args['stdin'] = stdin
-
     return subprocess.Popen(cmd, **args)