The possible cause for this error is because there has not been a right API call made to Tiingo/Alphavantage.
Hence the RestTemplate.getForObject returns a Null Pointer Exception.
Make sure you are making the right API call.
If this is a specific issue occurring with your Tiingo API call, you can check the PortfolioManagerImpl.java file,
Check your buildUri() function, andre-inspect your API call.