code: public static SpanId fromBytes(byte[] src, int srcOffset) {
      Utils.checkNotNull(src, "src");
      return new SpanId(BigendianEncoding.longFromByteArray(src, srcOffset));
    }
docs: Returns a {@code SpanId} whose representation is copied from the {@code src} beginning at the
  {@code srcOffset} offset.
  
  @param src the buffer where the representation of the {@code SpanId} is copied.
  @param srcOffset the offset in the buffer where the representation of the {@code SpanId}
  begins.
  @return a {@code SpanId} whose representation is copied from the buffer.
  @throws NullPointerException if {@code src} is null.
  @throws IndexOutOfBoundsException if {@code srcOffset+SpanId.SIZE} is greater than {@code
  src.length}.
  @since 0.5