LazyStringMapTemplate::get returns Nullptr wich is not in oatpp.io Documentation

[tibersam]

Hi all,

Thank you for your work on oatpp.

In my Application i am analyzing the provided Content-Type Header attribute during a multipart/form-data post request of the overall request and the different parts. At first i only looked up the Documentation from the website.
For LazyStringMapTemplate::get it states the return is "Get value as oatpp::String". This tempted my to use the empty function of strings to check if the key Content-Type exists.
I assumed if the key is not present an empty string is returned. The actual returned nullptr crashed the application if the field was not present.

Is it possible to either update the documentation to state that a nullptr is returned the key is not valid or to return an empty string instead of nullptr?

oatpp/src/oatpp/core/data/share/LazyStringMap.hpp

Lines 222 to 240 in 17ef2a7

	/**
	* Get value as &id:oatpp::String;.
	* @param key
	* @return
	*/
	String get(const Key& key) const {
	std::lock_guard<concurrency::SpinLock> lock(m_lock);
	auto it = m_map.find(key);
	if(it != m_map.end()) {
	it->second.captureToOwnMemory();
	return it->second.getMemoryHandle();
	}
	return nullptr;
	}