I'm unsure what's the shortest and most robust way to check whether a Text field is blank / empty?

/*1*/ Boolean isBlank = record.txt_Field__c == ''; /*2*/ Boolean isBlank = record.txt_Field__c == null; /*3*/ Boolean isBlank = record.txt_Field__c.trim() == ''; /*4*/ Boolean isBlank = record.txt_Field__c.size() == 0;