Update specs/agents/universal-profiling-integration.md

Co-authored-by: Jonas Kunz <jonas.kunz@elastic.co>

specs/agents/universal-profiling-integration.md

@@ -191,7 +191,7 @@ samples-delay-ms      | uint32
 host-id               | utf8-str
 
 * *samples-delay-ms*: A sane upper bound of the usual time taken in milliseconds by the profiling agent between the collection of a stacktrace and it being written to the apm-agent via the [messaging socket](#cpu-profiler-trace-correlation-message). The APM-agent will assume that all profiling data related to a span has been written to the socket if a span ended at least the provided duration ago. Note that this value doesn't need to be a hard a guarantee, but it should be the 99% case so that profiling data isn't distorted in the expected case.
-* *host-id*: The [`host.id` resource attribute](https://opentelemetry.io/docs/specs/semconv/attributes-registry/host/) is an optional argument used to correlate profiling data by the profiling agent. If an APM-agent is already sending a `host.id` it MUST print a warning if the `host.id` is different and otherwise ignore the value received by the profiling agent. A mismatch will lead to certain correlation features (e.g. cost and CO2 consumption) not working. If an APM-agent does not collect the `host.id` by itself, it MUST start sending the `host.id` after receiving it from the profiling agent to ensure aforementioned correlation features work correctly.
+* *host-id*: The [`host.id` resource attribute](https://opentelemetry.io/docs/specs/semconv/attributes-registry/host/) is an optional argument (the string may have a length of zero) used to correlate profiling data by the profiling agent. If an APM-agent is already sending a `host.id` it MUST print a warning if the `host.id` is different and otherwise ignore the value received by the profiling agent. A mismatch will lead to certain correlation features (e.g. cost and CO2 consumption) not working. If an APM-agent does not collect the `host.id` by itself, it MUST start sending the `host.id` after receiving a non-empty `host.id` from the profiling agent to ensure aforementioned correlation features work correctly.
 
 
 ## CPU Profiler Trace Correlation Message