MINIFICPP-2787 Do not encrypt empty properties and parameters

[fgerlits]

This also fixes a bug: if a sensitive value was set as

  sensitive_property:

instead of

  sensitive_property: ""

in a YAML flow configuration, then the value was null instead of an empty string, and it got expanded to the string "null", and then encrypted.

https://issues.apache.org/jira/browse/MINIFICPP-2787

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[szaszm]

I would represent expected alternatives like this. What do you think?

Suggested change

	if (!expected) {
	return "error: " + Catch::Detail::stringify(expected.error());
	}
	if constexpr (!std::is_void_v<T>) {
	return Catch::Detail::stringify(*expected);
	}
	return "OK";
	if (expected.has_value() && std::is_void_v<T>) {
	return "expected(void)";
	} else if (expected.has_value()) {
	return fmt::format("expected({})", Catch::Detail::stringify(expected.value()));
	} else {
	return fmt::format("unexpected({})", Catch::Detail::stringify(expected.error()));
	}

[fgerlits]

Not sure -- I think

  CHECK(processor_after->getProperty("invokehttp-proxy-password") == "")
with expansion:
  "null" == ""

reads better than

  CHECK(processor_after->getProperty("invokehttp-proxy-password") == "")
with expansion:
  expected("null") == ""

but the second option has its advantages, too. If you still like the second option better after sleeping on it, I don't mind changing it.