fix bug in slurm_runner for empty commands (#819)

- fix bug due to joining of NoneType (no command specified)
- change `dockerfile` variable name to `build_ctx_path` to be consistent with other runners

cli/popper/runner_slurm.py

@@ -104,12 +104,12 @@ def run(self, step):
         cid = pu.sanitized_name(step['name'], self._config.wid)
         cmd = []
 
-        build, img, tag, dockerfile = self._get_build_info(step)
+        build, img, tag, build_ctx_path = self._get_build_info(step)
 
         cmd.append(f'docker rm -f {cid} || true')
 
         if build:
-            cmd.append(f'docker build -t {img}:{tag} {dockerfile}')
+            cmd.append(f'docker build -t {img}:{tag} {build_ctx_path}')
         elif not self._config.skip_pull and not step.get('skip_pull', False):
             cmd.append(f'docker pull {img}:{tag}')
 
@@ -138,15 +138,18 @@ def _create_cmd(self, step, img, cid):
         for env_key, env_val in container_args.pop('environment').items():
             cmd.append(f'-e {env_key}={env_val}')
 
-        command = ' '.join(container_args.pop('command', []))
+        command = container_args.pop('command')
         image = container_args.pop('image')
 
         # anything else is treated as a flag
         for k, v in container_args.items():
             cmd.append(pu.key_value_to_flag(k, v))
 
         # append the image and the commands
-        cmd.append(f'{image} {command}')
+        cmd.append(image)
+
+        if command:
+            cmd.append(' '.join(command))
 
         return ' '.join(cmd)
 

cli/test/test_runner_slurm.py

@@ -284,6 +284,25 @@ def test_run(self, mock_kill):
 docker create --name popper_1_123abc --workdir /workspace --entrypoint cat -v /w:/workspace -v /var/run/docker.sock:/var/run/docker.sock -v /path/in/host:/path/in/container -e FOO=bar --privileged --hostname popper.local --domainname www.example.org popperized/bin:master README.md
 docker start --attach popper_1_123abc""")
 
+        with WorkflowRunner(config) as r:
+            wf = YMLWorkflow("""
+            version: '1'
+            steps:
+            - uses: 'popperized/bin/sh@master'
+              runs: [ls]
+            """)
+            wf.parse()
+            r.run(wf)
+
+        with open('/tmp/popper/slurm/popper_1_123abc.sh', 'r') as f:
+            content = f.read()
+            self.assertEqual(content,
+                             f"""#!/bin/bash
+docker rm -f popper_1_123abc || true
+docker build -t popperized/bin:master {os.environ['HOME']}/.cache/popper/123abc/github.com/popperized/bin/sh
+docker create --name popper_1_123abc --workdir /workspace --entrypoint ls -v /w:/workspace -v /var/run/docker.sock:/var/run/docker.sock -v /path/in/host:/path/in/container -e FOO=bar --privileged --hostname popper.local --domainname www.example.org popperized/bin:master
+docker start --attach popper_1_123abc""")
+
 
 class TestSlurmSingularityRunner(unittest.TestCase):
     def setUp(self):