* This method is from opentracing-java. {@see https://github.com/opentracing/opentracing-java/blob/release-0.20.9/opentracing-api/src/main/java/io/opentracing/Span.java#L91}
* <p> Log key:value pairs to the Span with the current walltime timestamp. <p> <p><strong>CAUTIONARY NOTE:</strong>
* not all Tracer implementations support key:value log fields end-to-end. Caveat emptor. <p> <p>A contrived example
* (using Guava, which is not required):
* <pre>{@code
* span.log(
* ImmutableMap.Builder<String, Object>()
* .put("event", "soft error")
* .put("type", "cache timeout")
* .put("waited.millis", 1500)
* .build());
* }</pre>
*
* @param fields key:value log fields. Tracer implementations should support String, numeric, and boolean values;
* This method is from opentracing-java. {@see https://github.com/opentracing/opentracing-java/blob/release-0.20.9/opentracing-api/src/main/java/io/opentracing/Span.java#L120}
* <p> Record an event at the current walltime timestamp. <p> Shorthand for <p>