Amplifying photodiode current with BJT transistor
A photodiode doesn’t have to be biased; it will try and force a photo current into whatever circuit it is connected to. In your emitter follower circuit if you removed Rb, there will be a path for photo current to flow through the base emitter junction, through the emitter resistor and back to the negative terminal on the supply. The base emitter junction behaves like a forward biased diode and drops around 0.7 volts in a typical circuit but, this can range from a couple of hundred milli volts to around 1 volt (depending on the circuit).
You can put a resistor in the collector and short emitter to ground and you get a very high gain amplifier. Because base and emitter conduct at typically around 0.7 volts (as per (1) explanation), you won’t ever see 1.2 volts. Yes it can be unstable and be influenced by temperature and light changes (sometimes) and, that is why it tends not to get used like that in engineered circuits.