Allow unset of entrypoint (resolves #5582)

When an empty string is passed to the 'entrypoint' parameter, for example
`docker-compose run --entrypoint='' ...`
OR
`docker-compose run --entrypoint '' ...`
It allows the default entrypoint to be overriden by empty value.

Signed-off-by: Ganesh Satpute <[email protected]>

compose/cli/main.py

@@ -1232,8 +1232,7 @@ def build_container_options(options, detach, command):
     if options['--label']:
         container_options['labels'] = parse_labels(options['--label'])
 
-    if options['--entrypoint']:
-        container_options['entrypoint'] = options.get('--entrypoint')
+    _build_container_entrypoint_options(container_options, options)
 
     if options['--rm']:
         container_options['restart'] = None
@@ -1260,6 +1259,16 @@ def build_container_options(options, detach, command):
     return container_options
 
 
+def _build_container_entrypoint_options(container_options, options):
+    if options['--entrypoint']:
+        if options['--entrypoint'].strip() == '':
+            # Set an empty entry point. Refer https://github.com/moby/moby/pull/23718
+            log.info("Overriding the entrypoint")
+            container_options['entrypoint'] = [""]
+        else:
+            container_options['entrypoint'] = options.get('--entrypoint')
+
+
 def run_one_off_container(container_options, project, service, options, toplevel_options,
                           project_dir='.'):
     if not options['--no-deps']: