Population Layout Bug for Electricity Only Studies

[ktehranchi]

Checklist

• I am using the current master branch
• I am running on an up-to-date pypsa-usa environment. Update via conda env update -f envs/environment.yaml

The Issue

def pop_layout_input(wildcards):
    if wildcards["sector"] != "E":
        return RESOURCES + "{interconnect}/pop_layout_elec_s{simpl}_c{clusters}.csv"
    else:
        return ""

return "" is incorrect syntax - switch to return []

Steps To Reproduce

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Expected Behavior

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Error Message

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Anything else?

No response