code: public static String getHttpMethod(Span span) {
          if (isHttp(span)) {
              BinaryAnnotation ba = span.getBinaryAnnotation("http.method");
              String httpMethod = null;
              if (ba != null) {
                  httpMethod = ba.getValue().toUpperCase();
              } else if (span.getName() != null) {
                  httpMethod = span.getName().toUpperCase();
              }
  
              if (HTTP_METHODS.contains(httpMethod)) {
                  return httpMethod;
              }
          }
  
          return null;
      }
docs: Derives HTTP operation from Span's binary annotations.
  
  @param span the span
  @return HTTP method