[Bug] sankey chart tooltip has no title when there is on one node in depth 0

Version

2.0.5

Link to Minimal Reproduction

null

Steps to Reproduce

const spec = {
type: 'sankey',
data: [
{
values: [
{
nodes: [
{ nodeName: "Agricultural 'waste'" },
{ nodeName: 'Bio-conversion' },
{ nodeName: 'Liquid' },
{ nodeName: 'Losses' },
{ nodeName: 'Solid' },
{ nodeName: 'Gas' },
{ nodeName: 'Biofuel imports' },
{ nodeName: 'Biomass imports' },
{ nodeName: 'Coal imports' },
{ nodeName: 'Coal' },
{ nodeName: 'Coal reserves' },
{ nodeName: 'District heating' },
{ nodeName: 'Industry' },
{ nodeName: 'Heating and cooling - commercial' },
{ nodeName: 'Heating and cooling - homes' },
{ nodeName: 'Electricity grid' },
{ nodeName: 'Over generation / exports' },
],
links: [
{
"source": 0,
"target": 1,
"value": 241202
},
{
"source": 0,
"target": 2,
"value": 49988
},
{
"source": 0,
"target": 3,
"value": 2190
},
{
"source": 0,
"target": 4,
"value": 20036
},
{
"source": 0,
"target": 5,
"value": 13774
},
{
"source": 1,
"target": 6,
"value": 39093
},
{
"source": 1,
"target": 7,
"value": 37043
},
{
"source": 1,
"target": 8,
"value": 160770
},
{
"source": 1,
"target": 9,
"value": 4298
},
{
"source": 2,
"target": 6,
"value": 11214
},
{
"source": 2,
"target": 7,
"value": 18377
},
{
"source": 2,
"target": 8,
"value": 1152
},
{
"source": 2,
"target": 9,
"value": 19245
},
{
"source": 3,
"target": 7,
"value": 134
},
{
"source": 3,
"target": 8,
"value": 1722
},
{
"source": 3,
"target": 9,
"value": 334
},
{
"source": 4,
"target": 7,
"value": 15958
},
{
"source": 4,
"target": 8,
"value": 3298
},
{
"source": 4,
"target": 9,
"value": 780
},
{
"source": 5,
"target": 7,
"value": 683
},
{
"source": 5,
"target": 8,
"value": 13035
},
{
"source": 5,
"target": 9,
"value": 56
},
{
"source": 6,
"target": 10,
"value": 39004
},
{
"source": 7,
"target": 11,
"value": 46571
},
{
"source": 7,
"target": 12,
"value": 29468
},
{
"source": 8,
"target": 12,
"value": 183345
},
{
"source": 12,
"target": 13,
"value": 176318
},
{
"source": 12,
"target": 14,
"value": 36495
},
{
"source": 13,
"target": 15,
"value": 164902
},
{
"source": 13,
"target": 16,
"value": 11633
},
{
"source": 9,
"target": 10,
"value": 0
},
{
"source": 10,
"target": 13,
"value": 0
},
{
"source": 11,
"target": 13,
"value": 0
},
{
"source": 14,
"target": 16,
"value": 0
}
]
}
]
}
],
categoryField: 'nodeName',
valueField: 'value',
sourceField: 'source',
targetField: 'target',

nodeAlign: 'justify',
nodeGap: 8,
nodeWidth: 10,
minNodeHeight: 4,

title: {
text: 'How energy is converted or transmitted before being consumed or lost',
subtext: 'Data: Department of Energy & Climate Change via Tom Counsell',
subtextStyle: {
fontSize: 12
}
},

label: {
visible: true,
style: {
fontSize: 10
}
},

node: {
state: {
hover: {
stroke: '#333333'
},
selected: {
fill: '#dddddd',
stroke: '#333333',
lineWidth: 1,
brighter: 1,
fillOpacity: 1
}
}
},

link: {
state: {
hover: {
fillOpacity: 1
},
selected: {
fill: '#dddddd',
stroke: '#333333',
lineWidth: 1,
brighter: 1,
fillOpacity: 1
}
}
}
};

const vchart = new VChart(spec, { dom: CONTAINER_ID });
vchart.renderSync();

// Just for the convenience of console debugging, DO NOT COPY!
window['vchart'] = vchart;

Current Behavior

Expected Behavior

has title like this

Environment

- OS:
- Browser:
- Framework:

Any additional comments?

No response