prefer None over placeholders

When data is unavailable, unknown, or invalid, return None instead of placeholder strings like “Unknown”, “Unspecified”, or “???”. This makes the absence of data explicit and prevents downstream code from treating placeholder values as legitimate data.

Apply this pattern when:

• API responses contain unknown/invalid values that should be mapped to None
• Optional device attributes are missing and would otherwise get placeholder defaults
• Enum values are unrecognized and should be treated as missing rather than preserved as strings

Example:

# Avoid placeholder defaults
model=host_data.get("devmodel")  # Returns None if missing
# Instead of:
model=host_data.get("devmodel", "Unknown")

# Map invalid values to None
return {"???": None, "UNSPECIFIED": None}.get(raw_value, raw_value)
# Instead of:
return {"???": "unknown"}.get(raw_value, raw_value)

Always pair with null checks:

if self._device.data["_state"]["lastComms"] is not None:
    self._last_comms = dt_util.utc_from_timestamp(
        self._device.data["_state"]["lastComms"]
    )

This approach makes data availability explicit, prevents confusion between actual values and placeholders, and enables proper null safety patterns throughout the codebase.