code: @Nullable
    public <A extends AbstractValue<A>, S extends Store<S>, T extends TransferFunction<A, S>>
        A expressionDataflow(TreePath exprPath, Context context, T transfer) {
      AnalysisResult<A, S> analysisResult = resultForExpr(exprPath, context, transfer);
      return analysisResult == null ? null : analysisResult.getValue(exprPath.getLeaf());
    }
docs: Run the {@code transfer} dataflow analysis to compute the abstract value of the expression
  which is the leaf of {@code exprPath}.
  
  @param exprPath expression
  @param context Javac context
  @param transfer transfer functions
  @param <A> values in abstraction
  @param <S> store type
  @param <T> transfer function type
  @return dataflow value for expression