code: def filter_by_gene_expression(
              self,
              gene_expression_dict,
              min_expression_value=0.0):
          
          return self.filter_above_threshold(
              key_fn=lambda effect: effect.gene_id,
              value_dict=gene_expression_dict,
              threshold=min_expression_value)
docs: Filters effects to those which have an associated gene whose
          expression value in the gene_expression_dict argument is greater
          than min_expression_value.
  
          Parameters
          ----------
          gene_expression_dict : dict
              Dictionary mapping Ensembl gene IDs to expression estimates
              (either FPKM or TPM)
  
          min_expression_value : float
              Threshold above which we'll keep an effect in the result collection