Measurements using `get_connections` fails when sites are unset and no pin map is provided

Bug Report

• Running the Python measurements with get_connections without a pin map and with sites not configured in the pin map context results in a measurement failure, accompanied by the following exception:
  

Repro or Code Sample

• Create a Python Measurement Client for niscope_acquire_waveform.
• With no pin map, set pin_map_context to PinMapContext(pin_map_id="", sites=[]).
• Call measure() API.

Expected Behavior

Return the the output of the measurement.

Current Behavior

Measurement fails with an exception.

Possible Solution

https://github.com/ni/measurement-plugin-python/pull/915#discussion_r1771833680

Context

https://github.com/ni/measurement-plugin-python/pull/915#discussion_r1771745886

Your Environment

• OS & Device: Windows
• ni-measurement-plugin-sdk-service version: 2.1.0-dev0 - main
• MeasurementLink version: 2024 Q3
• Python version: 3.9

AB#2865897

Start with the Python measurement client and the examples/niscope_acquire_waveform measurement, then trace measure() and get_connections() with PinMapContext(pin_map_id="", sites=[]). Reproduce the failure without a pin map; done means measure() returns the measurement output instead of raising the reported exception.