diff --git a/checker.py b/checker.py
index 3c1f9a0..38a3a34 100644
--- a/checker.py
+++ b/checker.py
@@ -46,7 +46,7 @@ def main(files: List[str], draw_cfg: str = "",
     parser.add_argument("files", nargs='*', help="Path to IEC source files")
     parser.add_argument("--draw-cfg", type=str,
                         help="Save control flow graph image at the selected path")
-    parser.add_argument("-b","--binary", default=os.path.join("output", "bin", "iec_checker"),
+    parser.add_argument("-b", "--binary", default=os.path.join("output", "bin", "iec_checker"),
                         help="File path to the OCaml binary")
     args = parser.parse_args()
     sys.exit(main(args.files, args.draw_cfg, args.binary))
diff --git a/src/python/core.py b/src/python/core.py
index c752269..cb881e3 100644
--- a/src/python/core.py
+++ b/src/python/core.py
@@ -52,7 +52,7 @@ def run_checker(file_path: str, binary: str = binary_default,
 
 
 def run_checker_full_out(file_path: str, binary: str = binary_default,
-                *args) -> Tuple[int, str]:
+                         *args) -> Tuple[int, str]:
     """Run iec-checker core for a given file and capture the whole output.
     No extra options will be set by default."""
     p = subprocess.Popen([binary, *args, file_path],
diff --git a/src/python/dump.py b/src/python/dump.py
index 3dfe1e9..753c6a1 100644
--- a/src/python/dump.py
+++ b/src/python/dump.py
@@ -4,7 +4,7 @@
 import os
 import logging
 from dataclasses import dataclass
-from typing import List
+from typing import List, Optional
 import ijson
 
 from .om import Scheme
@@ -30,7 +30,7 @@ class DumpManager:
 
     def __init__(self, dump_path: str):
         self.dump_path: str = dump_path
-        self.scheme: Scheme = None
+        self.scheme: Optional[Scheme] = None
 
     def __enter__(self):
         self.scheme = self.mk_scheme()
@@ -51,6 +51,8 @@ def mk_scheme(self) -> Scheme:
         with open(self.dump_path, 'rb') as f:
             for item in ijson.items(f, ""):
                 scheme = Scheme.from_dict(item)
+        if not scheme:
+            raise Exception(f"Cannot parse JSON scheme from {self.dump_path}")
         return scheme
 
     def remove_dump(self):
diff --git a/src/python/om.py b/src/python/om.py
index c4ee34f..40f9365 100644
--- a/src/python/om.py
+++ b/src/python/om.py
@@ -1,7 +1,6 @@
 """Object model
 The Object model represents IR data from the iec-checker core.
 """
-
 from dataclasses import dataclass
 from typing import List, Dict, Set