code: public final Span getCurrentSpan() {
      Span currentSpan = CurrentSpanUtils.getCurrentSpan();
      return currentSpan != null ? currentSpan : BlankSpan.INSTANCE;
    }
docs: Gets the current Span from the current Context.
  
  <p>To install a {@link Span} to the current Context use {@link #withSpan(Span)} OR use {@link
  SpanBuilder#startScopedSpan} methods to start a new {@code Span}.
  
  <p>startSpan methods do NOT modify the current Context {@code Span}.
  
  @return a default {@code Span} that does nothing and has an invalid {@link SpanContext} if no
  {@code Span} is associated with the current Context, otherwise the current {@code Span}
  from the Context.
  @since 0.5