code: @SuppressWarnings("unchecked")
      public Map<String, String> getSystemJavaxPersistenceOverrides() {
          if(propertyOverridesExist()) {
              // we make use of a type cast hack to convert Properties to a Map
              return mergeFilteredMaps(System.getenv(), (Map) System.getProperties());
          }
          return null;
      }
docs: Resolves a Union of System.env and System.getProperties() where the KeyValue-Pairs of the later have precedence.
  
  @return Map or null if none of the following Properties exists:
  javax.persistence.jdbc.driver,javax.persistence.jdbc.url, javax.persistence.jdbc.user, javax.persistence.jdbc.password