Invalid child_of option. Expected Span or SpanContext, got NULL

[NikolaySav]

Invalid child_of option. Expected Span or SpanContext, got NULL

opentracing/opentracing/src/OpenTracing/StartSpanOptions.php(164): OpenTracing\Exceptions\InvalidSpanOption::forInvalidChildOf(NULL)
opentracing/opentracing/src/OpenTracing/StartSpanOptions.php(49): OpenTracing\StartSpanOptions::buildChildOf(NULL)

fails on null

#89

[jukylin]

same issues #88

[sunlongv520]

我也遇到了