Option Indicator Example Algorithms Throw Errors

[DerekMelchin]

Expected Behavior

The example algorithms in https://www.quantconnect.com/docs/v2/writing-algorithms/indicators/supported-indicators/gamma#02-Using-G-Indicator run without error.

Actual Behavior

Runtime Error: 'int' object has no attribute 'Current'
  at OnData
    self.Plot("Gamma" in main.py: line 19

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