code: public String get(final String key) {
          if (key == null || initProps == null)
              return null;
  
          String value = initProps.get(key);
          if (value == null) {
              try {
                  value = AccessController.doPrivileged(new java.security.PrivilegedExceptionAction<String>() {
                      @Override
                      public String run() throws Exception {
                          return System.getProperty(key);
                      }
                  });
              } catch (Exception ex) {
              }
          }
  
          return value;
      }
docs: Get value from initial configuration properties. If property is not
  present in initial/framework properties, try finding it in system
  properties.
  
  @param key
  Property key
  @return Object value, or null if not found.