fix: Set empty style porperty values to undefined instead of empty string

resolves #271

Author: pekarja5

src/components/ReactSlider/ReactSlider.jsx

@@ -964,7 +964,7 @@ class ReactSlider extends React.Component {
         const style = {
             position: 'absolute',
             touchAction: 'none',
-            willChange: this.state.index >= 0 ? this.posMinKey() : '',
+            willChange: this.state.index >= 0 ? this.posMinKey() : undefined,
             zIndex: this.state.zIndices.indexOf(i) + 1,
         };
         style[this.posMinKey()] = `${offset}px`;
@@ -974,7 +974,8 @@ class ReactSlider extends React.Component {
     buildTrackStyle(min, max) {
         const obj = {
             position: 'absolute',
-            willChange: this.state.index >= 0 ? `${this.posMinKey()},${this.posMaxKey()}` : '',
+            willChange:
+                this.state.index >= 0 ? `${this.posMinKey()},${this.posMaxKey()}` : undefined,
         };
         obj[this.posMinKey()] = min;
         obj[this.posMaxKey()] = max;

src/components/ReactSlider/__tests__/__snapshots__/ReactSlider.test.js.snap

@@ -18,7 +18,7 @@ exports[`<ReactSlider> can render 1`] = `
         "left": 0,
         "position": "absolute",
         "right": 0,
-        "willChange": "",
+        "willChange": undefined,
       }
     }
   />
@@ -29,7 +29,7 @@ exports[`<ReactSlider> can render 1`] = `
         "left": 0,
         "position": "absolute",
         "right": 0,
-        "willChange": "",
+        "willChange": undefined,
       }
     }
   />
@@ -48,7 +48,7 @@ exports[`<ReactSlider> can render 1`] = `
         "left": "0px",
         "position": "absolute",
         "touchAction": "none",
-        "willChange": "",
+        "willChange": undefined,
         "zIndex": 1,
       }
     }