code: function drawEmptyDataLine() {
              let emptyDataLine = d3Shape.line()
                  .x( (d) => xScale(d.date) )
                  .y( () => yScale(0) - 1 );
  
              let chartGroup = svg.select('.chart-group');
  
              chartGroup
                .append('path')
                  .attr('class', 'empty-data-line')
                  .attr('d', emptyDataLine(dataByDateFormatted))
                  .style('stroke', 'url(#empty-data-line-gradient)');
  
              chartGroup
                .append('linearGradient')
                  .attr('id', 'empty-data-line-gradient')
                  .attr('gradientUnits', 'userSpaceOnUse')
                  .attr('x1', 0)
                  .attr('x2', xScale(data[data.length - 1].date))
                  .attr('y1', 0)
                  .attr('y2', 0)
                  .selectAll('stop')
                  .data([
                      {offset: '0%', color: lineGradient[0]},
                      {offset: '100%', color: lineGradient[1]}
                  ])
                  .enter()
                    .append('stop')
                      .attr('offset', ({offset}) => offset)
                      .attr('stop-color', ({color}) => color);
          }
docs: Draws an empty line when the data is all zero
  @private