code: def _compute_qual_histogram(single_var_stats):
      """Compute a histogram over variant quality (QUAL column in VCF).
  
      Args:
        single_var_stats: list of VariantStats objects.
  
      Returns:
        histogram of variant quality scores.
      """
      quals = [round(v.qual, 4) for v in single_var_stats]
  
      if quals:
          bin_range = (
              _round_down(min(quals)),
              _round_up(max(quals) + 1),
          )
          counts, bins = np.histogram(
              quals, range=bin_range, bins=bin_range[1] - bin_range[0]
          )
          hist = _format_histogram_for_vega(counts, bins)
          return [x for x in hist if x["c"] > 0]
      else:
          return []
  
imports: import collections
  import itertools
  import math
  import numpy
  from third_party.nucleus.util import variant_utils
  from third_party.nucleus.util import variantcall_utils
  from deepvariant import vcf_stats_vis
label_desc: Use image node_id 12 for calling a global function with example usage: _compute_qual_histogram(single_var_stats) and returns: unknown, list