fix(labels): Fix index argument for nullish value

Index argument passed to data.labels.format
should be couning nullish value

Fix #3547

src/ChartInternal/internals/text.ts

@@ -208,7 +208,7 @@ export default {
 				}
 
 				value = $$.isTreemapType(d) ? $$.treemapDataLabelFormat(d)(node) :
-					$$.dataLabelFormat(d.id)(value, d.id, i, texts);
+					$$.dataLabelFormat(d.id)(value, d.id, d.index, texts);
 
 				if (isNumber(value)) {
 					this.textContent = value;

test/internals/text-spec.ts

@@ -561,6 +561,8 @@ describe("TEXT", () => {
 			});
 
 			describe("as function", () => {
+				const temp: any = [];
+
 				before(() => {
 					args = {
 						data: {
@@ -593,6 +595,29 @@ describe("TEXT", () => {
 						expect(d3Select(this).text()).to.equal("");
 					});
 				});
+
+				it("set options", () => {
+					args = {
+						data: {
+							columns: [
+								["data1", 10, 100, null, 150, 200]
+							],
+							labels: {
+								format: (value, seriesName, columnIndex) => {																	
+									if (seriesName) {
+										temp.push(columnIndex);
+									}
+
+									return value;
+								}
+							}
+						}
+					}
+				});
+
+				it("index argument should count nullish value", () => {
+					expect(temp).to.be.deep.equal([0, 1, 3, 4]);					
+				});
 			});
 		});