code: public Property getDeclaredProperty(String propertyName) {
          if (propertyName == null) {
              throw new NullPointerException("Cannot get a declared property with a 'null' propertyName.");
          }
  
          return declaredProperties.get(propertyName);
      }
docs: Returns a single declared property of the analized class or interface,
  if present, else {@code null}.
  
  @param propertyName the name of the declared property to retrieve
  @return the declared {@link Property} searched, or {@code null} if not found
  @throws NullPointerException if propertyName parameter is {@code null}