Use of `NaN` in mesh.json output files

[thomaszwagerman]

In meshes where a parameter is missing:

"cellboxes": [
        {
            "geometry": "POLYGON ((-110 -80, -110 -77.5, -105 -77.5, -105 -80, -110 -80))",
            "cx": -107.5,
            "cy": -78.75,
            "dcx": 2.5,
            "dcy": 1.25,
            "elevation": 2000.0,
            "SIC": NaN,
            "uC": NaN,
            "vC": NaN,
            "thickness": 0.65,
            "density": 920.0,
            "id": "0"
        },
]

NaN is used to indicate null. NaN is not valid JSON, and causes issues with any PostgreSQL ingestion.

Ideally this is converted to None (ie, null in JSON), which is a valid JSON value.

[thomaszwagerman]

bas-logist/PolarRoute-server#120 contains mesh cleaning code which deals with this for the server.

Should this be fixed on MeshiPhi in the future PolarRoute-server devs should be notified so it can be cleaned up.

I would say this is a high-priority fix, this causes various issues in different places.