Background subtraction fails on science frames

[gmbrandt]

We turned background subtraction off for all frames in PR #53 because it fails on science and traces. Some issue to do with negative fluxes.

As of PR #53, background subtraciton is only on for stacked lampflats.

Stack trace:

2021-03-17 14:25:14.453 INFO: stages: Running banzai.stages.TraceRefiner | {"filename": "lscnrs01-fa09-20190709-lampflat-bin1x1-110.fits", "site": "lsc", "instrument": "nres01", "epoch": "20190709", "request_num": "1854702", "obstype": "LAMPFLAT", "filter": null, "processName": "MainProcess"} 2021-03-17 14:25:14.807 INFO: traces: Fitting a polynomial to order 1 | {"filename": "lscnrs01-fa09-20190709-lampflat-bin1x1-110.fits", "site": "lsc", "instrument": "nres01", "epoch": "20190709", "request_num": "1854702", "obstype": "LAMPFLAT", "filter": null, "processName": "MainProcess"} 2021-03-17 14:25:14.819 ERROR: stages: ['Traceback (most recent call last):\n', ' File "/home/mjohnson/.conda/envs/condaforbanzai/lib/python3.8/site-packages/banzai/stages.py", line 47, in run\n processed_image = self.do_stage(image_set)\n', ' File "/home/mjohnson/Documents/astro/nres/banzai-nres-own/banzai-nres/banzai_nres/traces.py", line 109, in do_stage\n refine_traces(image, weights=image.data,\n', ' File "/home/mjohnson/Documents/astro/nres/banzai-nres-own/banzai-nres/banzai_nres/traces.py", line 51, in refine_traces\n best_fit = fit_polynomial(y_center, y_center_errors, mask=y_center_errors == 0, x=x_center, order=5)\n', ' File "/home/mjohnson/Documents/astro/nres/banzai-nres-own/banzai-nres/banzai_nres/fitting.py", line 25, in fit_polynomial\n best_fit = fitter(model, x_to_fit, y_to_fit, weights=weights)\n', ' File "/home/mjohnson/.conda/envs/condaforbanzai/lib/python3.8/site-packages/astropy/modeling/fitting.py", line 263, in wrapper\n return func(self, model, x, y, z=z, **kwargs)\n', ' File "/home/mjohnson/.conda/envs/condaforbanzai/lib/python3.8/site-packages/astropy/modeling/fitting.py", line 582, in __call__\n x = self._map_domain_window(model_copy, x)\n', ' File "/home/mjohnson/.conda/envs/condaforbanzai/lib/python3.8/site-packages/astropy/modeling/fitting.py", line 467, in _map_domain_window\n model.domain = [x.min(), x.max()]\n', ' File "/home/mjohnson/.conda/envs/condaforbanzai/lib/python3.8/site-packages/numpy/core/_methods.py", line 34, in _amin\n return umr_minimum(a, axis, None, out, keepdims, initial, where)\n', 'ValueError: zero-size array to reduction operation minimum which has no identity\n'] | {"processName": "MainProcess"}