Is there an advantage one over the other? In my current project, using the index with the dot is questioned as bad practice, requesting to always use the index() function, my question is, is this really necessary? what are the reasons? I understand that sometimes it is good to control the default value and set a null.
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Yes, it is bad practice. Simple example is, if you don't have value for the field and you use dot, then the index will fail, means it won't handle null propely except in value and saveinto parameters. But index() function will handle nulls and if there is no value for the field it returns null.