class_docstr: A sampler that combines positive sampler and negative sampler.
docstr: Sample negative samples.
docstr_tok: ["Sample","negative","samples","."]
code: def _sample_neg(self, **kwargs):
      """Sample negative samples."""
      raise NotImplementedError
  
imports: from ..builder import BBOX_SAMPLERS, build_sampler
  from .base_sampler import BaseSampler
label_desc: Use image node_id 3 for calling the CombinedSampler obj's underlying member method code with example usage: obj._sample_neg() without return types