add assertion to make sure positions and positions_flat are not empty (#3387)

.pre-commit-config.yaml

@@ -17,7 +17,7 @@ repos:
     -   id: trailing-whitespace
     -   id: end-of-file-fixer
 -   repo: https://github.com/charliermarsh/ruff-pre-commit
-    rev: v0.1.13
+    rev: v0.6.2
     hooks:
     -   id: ruff
         types_or: [ python, pyi, jupyter ]

nerfstudio/fields/nerfacto_field.py

@@ -211,10 +211,15 @@ class NerfactoField(Field):
         # Make sure the tcnn gets inputs between 0 and 1.
         selector = ((positions > 0.0) & (positions < 1.0)).all(dim=-1)
         positions = positions * selector[..., None]
+
+        assert positions.numel() > 0, "positions is empty."
+
         self._sample_locations = positions
         if not self._sample_locations.requires_grad:
             self._sample_locations.requires_grad = True
         positions_flat = positions.view(-1, 3)
+
+        assert positions_flat.numel() > 0, "positions_flat is empty."
         h = self.mlp_base(positions_flat).view(*ray_samples.frustums.shape, -1)
         density_before_activation, base_mlp_out = torch.split(h, [1, self.geo_feat_dim], dim=-1)
         self._density_before_activation = density_before_activation