diff --git a/src/chart/line/LineView.ts b/src/chart/line/LineView.ts
index 3682d96512..e0de6d67de 100644
--- a/src/chart/line/LineView.ts
+++ b/src/chart/line/LineView.ts
@@ -345,6 +345,13 @@ function getVisualGradient(
             ? (outerColors[1] ? outerColors[1] : colorStops[stopLen - 1].color)
             : (outerColors[0] ? outerColors[0] : colorStops[0].color);
     }
+    if (!inRangeStopLen) {
+        // No color stops at all (e.g. when all visualMap pieces produce
+        // [-Infinity, Infinity] intervals, like `pieces: [{ lte: null }]`).
+        // Fall back to a single outer color or transparent so that we
+        // don't crash on `colorStopsInRange[0].coord` below. See #18066.
+        return outerColors[0] || outerColors[1] || 'transparent';
+    }
 
     const tinyExtent = 10; // Arbitrary value: 10px
     const minCoord = colorStopsInRange[0].coord - tinyExtent;
diff --git a/test/ut/spec/component/visualMap/setOption.test.ts b/test/ut/spec/component/visualMap/setOption.test.ts
index d132385eac..d90da36a43 100755
--- a/test/ut/spec/component/visualMap/setOption.test.ts
+++ b/test/ut/spec/component/visualMap/setOption.test.ts
@@ -287,4 +287,30 @@ describe('vsiaulMap_setOption', function () {
         done();
     });
 
+    // See https://github.com/apache/echarts/issues/18066
+    it('piecewiseWithNullBoundOnLineSeries', function (done) {
+        // Setting `lte: null` (or omitting both bounds) makes the piece
+        // interval [-Infinity, Infinity], which previously crashed
+        // line series rendering with
+        // "Cannot read properties of undefined (reading 'coord')".
+        expect(function () {
+            chart.setOption({
+                xAxis: {type: 'category', data: ['A', 'B', 'C', 'D']},
+                yAxis: {type: 'value'},
+                visualMap: {
+                    type: 'piecewise',
+                    pieces: [
+                        // lte set to null should be treated as no upper bound.
+                        {lte: null, color: 'red'}
+                    ]
+                },
+                series: [{
+                    type: 'line',
+                    data: [10, 20, 30, 40]
+                }]
+            });
+        }).not.toThrow();
+        done();
+    });
+
 });
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