pvlib.pvsystem.PVSystem states wrong default for module_type

[ramaroesilva]

Describe the bug
Within the pvlib.pvsystem.PVSystem documentation, the module_type parameter is stated to be glass_polymer as default, while in fact it the default value is None

To Reproduce
Steps to reproduce the behavior:

1. Run system = pvlib.pvsystem.PVSystem()
2. Print system variable
3. Check value for module_type

Expected behavior
Not sure if it is the documentation or the implementation that is wrong.

Screenshots
Initialization of the PVSystem class:

Versions:

• pvlib.__version__: 0.13.1
• pandas.__version__:
• python:

[markcampanelli]

Looks like the behavior when module_type is None is to fall back to the parameter defaults for the temperature function specified by the model parameter passed to Array.get_cell_temperature. Pretty convoluted!