Well, a logarithmic expression is just an exponential expression written from the point of the exponent.
now, ln is just a shorthand for the logarithm with a base "e" or euler's constant, so-called the "natural logarithm", now, let's use the exponential version of that here, and let's say equals an constant exponent of "k",
now, look closely, what "k" value, what exponent, negative or fraction or positive, will ever make "e" to 0? none, so one can say is "undefined".
now, ln is just a shorthand for the logarithm with a base "e" or euler's constant, so-called the "natural logarithm", now, let's use the exponential version of that here, and let's say equals an constant exponent of "k",
now, look closely, what "k" value, what exponent, negative or fraction or positive, will ever make "e" to 0? none, so one can say is "undefined".