Add test on processes_2_remove get empty string

tests/test_cli.py

@@ -26,3 +26,26 @@ class TestCall(unittest.TestCase):
                 output_dir=str(my_results),
                 name="https://github.com/blabla/toto:qsd!qsd%#sqdqsd"
             )
+
+    def test_with_processes_2_remove_empty_str(self):
+        with TemporaryDirectory() as my_temp_dir1, TemporaryDirectory() as my_temp_dir2:
+            my_results1 = pathlib.Path(my_temp_dir1) / "my_results"
+            cli(
+                "./wf_test/main.nf",
+                render_graphs=True,
+                output_dir=str(my_results1),
+                processes_2_remove="",
+            )
+            my_results2 = pathlib.Path(my_temp_dir2) / "my_results"
+            cli(
+                "./wf_test/main.nf",
+                render_graphs=True,
+                output_dir=str(my_results2),
+                processes_2_remove=None,
+            )
+            with open(my_results1 / 'graphs'/'specification_graph.png', 'rb') as f_spec1:
+                spec1 = f_spec1.read()
+            with open(my_results2 / 'graphs'/'specification_graph.png', 'rb') as f_spec2:
+                spec2 = f_spec2.read()
+
+            self.assertEqual(spec1, spec2)