Make sure extras is initialized as dict for Molecule (#305)

* Make sure extras is initialized as dict for Molecule

* Apply reformatting with black

qcelemental/models/molecule.py

@@ -350,6 +350,8 @@ def __init__(self, orient: bool = False, validate: Optional[bool] = None, **kwar
             kwargs = {**kwargs, **schema}  # Allow any extra fields
             validate = True
 
+        if "extras" not in kwargs:
+            kwargs["extras"] = {}
         super().__init__(**kwargs)
 
         # We are pulling out the values *explicitly* so that the pydantic skip_defaults works as expected

qcelemental/tests/test_molecule.py

@@ -686,6 +686,7 @@ def test_sparse_molecule_fields(mol_string, extra_keys):
         "fix_com",
         "fix_orientation",
         "provenance",
+        "extras",
     }
     mol = Molecule.from_data(mol_string)
 
@@ -724,3 +725,11 @@ def test_nonphysical_spec():
     assert compare_values([100.0], mol.masses, "nonphysical mass")
 
     print(mol.to_string(dtype="psi4"))
+
+
+def test_extras():
+    mol = qcel.models.Molecule(symbols=["He"], geometry=[0, 0, 0])
+    assert mol.extras is not None
+
+    mol = qcel.models.Molecule(symbols=["He"], geometry=[0, 0, 0], extras={"foo": "bar"})
+    assert mol.extras["foo"] == "bar"