code: public PostExecutionInterceptorContext mustPreserveCallTree(String reason) {
  		if (getSpanContext().getCallTree() == null) {
  			logger.info("Can't preserve the call tree because it has not been collected");
  		}
  		logger.debug("Must preserve call tree because {}", reason);
  		mustPreserveCallTree = true;
  		excludeCallTree = false;
  		return this;
  	}
docs: Makes sure that the call tree can't be {@linkplain #excludeCallTree excluded}
  <p>
  Note: if the call tree has not been collected, calling this method won't restore it.
  See also {@link PreExecutionInterceptorContext#mustCollectCallTree}
  
  @param reason the reason why the call tree should always be preserved (debug message)
  @return <code>this</code> for chaining