### What happened?

With the `otel` logging integration and semantic content events enabled (`OpenTelemetryConfig.enable_events` / `LITELLM_OTEL_INTEGRATION_ENABLE_EVENTS=true`), `OpenTelemetry._emit_semantic_logs` emits `gen_ai.content.prompt` / `gen_ai.content.completion` log records whose **attributes and body contain `None`**:

- `attrs["finish_reason"] = choice.get("finish_reason")` → `None` for streaming/partial choices - `attrs["gen_ai.system"]` → `None` when `custom_llm_provider` is unresolved - `body = msg.copy()` → raw message fields such as `content` / `tool_calls` are frequently `None`

OTLP `AnyValue` has no representation for `None`, so when the OTLP logs exporter encodes the record it raises and `BatchLogRecordProcessor` drops the **entire batch** — the content events are silently lost and the log fills with tracebacks.

### Traceback

``` Exception while exporting logs. .../opentelemetry/sdk/_logs/_internal/export/__init__.py in _export_batch .../opentelemetry/exporter/otlp/proto/grpc/_log_exporter/__init__.py in export .../opentelemetry/exporter/otlp/proto/common/_internal/_log_encoder/__init__.py in encode_logs .../opentelemetry/exporter/otlp/proto/common/…