diff --git a/spacy/errors.py b/spacy/errors.py
index 135aacf92..b6659a041 100644
--- a/spacy/errors.py
+++ b/spacy/errors.py
@@ -657,7 +657,9 @@ class Errors:
             "{nO} - cannot add any more labels.")
     E923 = ("It looks like there is no proper sample data to initialize the "
             "Model of component '{name}'. To check your input data paths and "
-            "annotation, run: python -m spacy debug data config.cfg")
+            "annotation, run: python -m spacy debug data config.cfg "
+            "and include the same config override values you would specify "
+            "for the 'spacy train' command.")
     E924 = ("The '{name}' component does not seem to be initialized properly. "
             "This is likely a bug in spaCy, so feel free to open an issue: "
             "https://github.com/explosion/spaCy/issues")
@@ -792,7 +794,7 @@ class Errors:
             "to token boundaries.")
     E982 = ("The `Token.ent_iob` attribute should be an integer indexing "
             "into {values}, but found {value}.")
-    E983 = ("Invalid key for '{dict}': {key}. Available keys: "
+    E983 = ("Invalid key(s) for '{dict}': {key}. Available keys: "
             "{keys}")
     E984 = ("Invalid component config for '{name}': component block needs either "
             "a key `factory` specifying the registered function used to "
diff --git a/spacy/tokens/_serialize.py b/spacy/tokens/_serialize.py
index 868eb3eab..5be66c801 100644
--- a/spacy/tokens/_serialize.py
+++ b/spacy/tokens/_serialize.py
@@ -8,7 +8,7 @@ from thinc.api import NumpyOps
 from .doc import Doc
 from ..vocab import Vocab
 from ..compat import copy_reg
-from ..attrs import SPACY, ORTH, intify_attr
+from ..attrs import SPACY, ORTH, intify_attr, IDS
 from ..errors import Errors
 from ..util import ensure_path, SimpleFrozenList
 
@@ -64,7 +64,11 @@ class DocBin:
 
         DOCS: https://spacy.io/api/docbin#init
         """
-        attrs = sorted([intify_attr(attr) for attr in attrs])
+        int_attrs = [intify_attr(attr) for attr in attrs]
+        if None in int_attrs:
+            non_valid = [attr for attr in attrs if intify_attr(attr) is None]
+            raise KeyError(Errors.E983.format(dict="attrs", key=non_valid, keys=IDS.keys())) from None
+        attrs = sorted(int_attrs)
         self.version = "0.1"
         self.attrs = [attr for attr in attrs if attr != ORTH and attr != SPACY]
         self.attrs.insert(0, ORTH)  # Ensure ORTH is always attrs[0]