fix: Ambiguous truth value of array during materialization#6259

alan-gauthier-jt

What this PR does / why we need it:

feast materialize crashes with ValueError: The truth value of an empty array is ambiguous when a scalar feature column contains an empty numpy array (e.g. np.array([])). This is a real-world scenario when a DataFrame row has a missing value represented as an empty array rather than None or np.nan.

Root cause: In _convert_scalar_values_to_proto (sdk/python/feast/type_map.py), the null check uses not pd.isnull(value) for every value in the loop. pd.isnull() is vectorised — when value is a numpy array, it returns a boolean array instead of a scalar. Applying Python's not operator to that array raises ValueError. The same issue exists in:

the BOOL scalar path (not pd.isnull(value) in a list comprehension)
the UNIX_TIMESTAMP early-return path (_python_datetime_to_int_timestamp(values) called with the raw values list, including any array-like values)
the sample type-validation check (sample == 0)

Fix: Before calling pd.isnull(), guard both scalar conversion loops (generic and BOOL) and the sample type-validation with an explicit isinstance(value, np.ndarray) check. Any array-like value in a scalar feature column is unmappable to a protobuf scalar field anyway, so it is safely treated as null → ProtoValue().

Input value Behaviour before Behaviour after

np.array([]) (empty)	ValueError crash	ProtoValue() (null)
np.array([np.nan, 1.0])	ValueError crash	ProtoValue() (null)
np.array([1.0, 2.0])	ValueError crash	ProtoValue() (null)
None	ProtoValue() (null)	unchanged
scalar non-null	ProtoValue(field=value)	unchanged

Which issue(s) this PR fixes:

Fixes #6255

Checks

I've made sure the tests are passing.
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Testing Strategy

Unit tests
Integration tests
Manual tests
Testing is not required for this change

Misc

let's extract this into small helper and use it everywhere to avoid duplication:

def _is_array_like(value: Any) -> bool: return isinstance(value, np.ndarray) or ( hasattr(value, "__len__") and not isinstance(value, (str, bytes)) )

Done

if else logic is going through all rows, better to pre filter first:

if feast_value_type == ValueType.UNIX_TIMESTAMP: out = [None] * len(values) clean_indices = [] clean_values = [] for i, value in enumerate(values): if _is_array_like(value) or value is None: out[i] = ProtoValue() else: clean_indices.append(i) clean_values.append(value) if clean_values: timestamps = _python_datetime_to_int_timestamp(clean_values) for i, ts in zip(clean_indices, timestamps): out[i] = ProtoValue(unix_timestamp_val=ts) return out

Thanks, I implemented your solution

ntkathole

@alan-gauthier-jt I think even better if we fix this at https://github.com/feast-dev/feast/blob/master/sdk/python/feast/type_map.py by adding logic for scalar columns, skip array-like values when picking a sample.

ntkathole

Thanks @alan-gauthier-jt looks good

alan-gauthier-jt requested a review from a team as a code owner April 10, 2026 13:30

alan-gauthier-jt force-pushed the fix-array-materialize branch from d35e16c to ea8f7da Compare April 10, 2026 13:32

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alan-gauthier-jt force-pushed the fix-array-materialize branch from ea8f7da to 33d1613 Compare April 10, 2026 14:45

HaoXuAI added the ok-to-test label Apr 11, 2026

This was referenced Apr 12, 2026

fix: handle empty numpy arrays in scalar proto conversion during materialization #6267

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ValueError: The truth value of an empty array is ambiguous during materialization #6255

Closed

ntkathole force-pushed the fix-array-materialize branch from 33d1613 to 8c0a6c6 Compare April 13, 2026 03:25

ntkathole reviewed Apr 13, 2026

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ntkathole changed the title fix: ambiguous truth value of array during materialization fix: Ambiguous truth value of array during materialization Apr 13, 2026

ntkathole reviewed Apr 13, 2026

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alan-gauthier-jt commented Apr 14, 2026

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Comment thread sdk/python/feast/type_map.py Show resolved Hide resolved

alan-gauthier-jt requested a review from ntkathole April 14, 2026 06:58

alan-gauthier-jt force-pushed the fix-array-materialize branch from 8d49e21 to 9037bdc Compare April 14, 2026 07:00

ntkathole approved these changes Apr 14, 2026

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alan-gauthier-jt added 2 commits April 14, 2026 13:00

fix: ambiguous truth value of array during materialization …

b18f71e

Signed-off-by: Alan Gauthier <alan.gauthier@jobteaser.com>

chore: refacto from pr feedback …

b91978e

Signed-off-by: Alan Gauthier <alan.gauthier@jobteaser.com>

ntkathole force-pushed the fix-array-materialize branch from 9037bdc to b91978e Compare April 14, 2026 07:31

-                      return [ProtoValue(unix_timestamp_val=ts) for ts in int_timestamps]  # type: ignore
+                      out = []
+                      for value in values:
+                          if isinstance(value, np.ndarray) or (

+                              out.append(ProtoValue())
+                          else:
+                              (ts,) = _python_datetime_to_int_timestamp([value])
+                              out.append(ProtoValue(unix_timestamp_val=ts))  # type: ignore

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fix: Ambiguous truth value of array during materialization#6259