code: public Object getValue(String key, DatabaseChangeLog changeLog) {
          ChangeLogParameter parameter = findParameter(key, changeLog);
          return (parameter != null) ? parameter.getValue() : null;
      }
docs: Return the value of a parameter
  
  @param key Name of the parameter
  @return The parameter value or null if not found. (Note that null can also be return if it is the parameter
  value. For strict parameter existence use {@link #hasValue(String, DatabaseChangeLog)}