Fix decode_params_tuple silently returning empty list when count > 0 but data is empty

The early return at line 102 fired unconditionally for empty data, even when
a non-zero count was externally provided. This caused silent data loss instead
of raising DecodeError for truncated/corrupt messages.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: antoineleclair

src/dqlitewire/tuples.py

@@ -100,6 +100,8 @@ def decode_params_tuple(
     """
     # Go writes nothing for empty params
     if len(data) == 0:
+        if count is not None and count > 0:
+            raise DecodeError(f"Expected data for {count} parameters, but data is empty")
         return [], 0
 
     if len(data) < 8:

tests/test_tuples.py

@@ -396,6 +396,27 @@ def test_decode_insufficient_data_for_header(self) -> None:
         with pytest.raises(DecodeError, match="Not enough data"):
             decode_params_tuple(b"\x01\x02\x03")
 
+    def test_decode_empty_data_with_nonzero_count_raises(self) -> None:
+        """Empty data with count > 0 should raise DecodeError, not return []."""
+        import pytest
+
+        from dqlitewire.exceptions import DecodeError
+
+        with pytest.raises(DecodeError, match="Expected data for 5 parameters"):
+            decode_params_tuple(b"", count=5)
+
+    def test_decode_empty_data_with_count_none_returns_empty(self) -> None:
+        """Empty data with count=None is legitimate (Go writes nothing for empty params)."""
+        result, consumed = decode_params_tuple(b"", count=None)
+        assert result == []
+        assert consumed == 0
+
+    def test_decode_empty_data_with_count_zero_returns_empty(self) -> None:
+        """Empty data with count=0 is legitimate."""
+        result, consumed = decode_params_tuple(b"", count=0)
+        assert result == []
+        assert consumed == 0
+
     def test_decode_insufficient_data_for_types(self) -> None:
         """Data too short for declared type count should raise DecodeError."""
         import pytest