fix: use strict null/undefined check for display value in single select

Empty string values should be treated as valid values (having a display value),
not as missing values. This fixes the content-has-value class not being applied
when the value is an empty string.

Co-Authored-By: Claude Opus 4.6 <[email protected]>

Author: zombieJ

src/SelectInput/Content/SingleContent.tsx

@@ -19,6 +19,7 @@ const SingleContent = React.forwardRef<HTMLInputElement, SharedContentProps>(
 
     const combobox = mode === 'combobox';
     const displayValue = displayValues[0];
+    const hasDisplayValue = displayValue !== null && displayValue !== undefined;
 
     // Implement the same logic as the old SingleSelector
     const mergedSearchValue = React.useMemo(() => {
@@ -34,7 +35,7 @@ const SingleContent = React.forwardRef<HTMLInputElement, SharedContentProps>(
       let style: React.CSSProperties | undefined;
       let titleValue: string | undefined;
 
-      if (displayValue && selectContext?.flattenOptions) {
+      if (hasDisplayValue && selectContext?.flattenOptions) {
         const option = selectContext.flattenOptions.find((opt) => opt.value === displayValue.value);
         if (option?.data) {
           className = option.data.className;
@@ -43,7 +44,7 @@ const SingleContent = React.forwardRef<HTMLInputElement, SharedContentProps>(
         }
       }
 
-      if (displayValue && !titleValue) {
+      if (hasDisplayValue && !titleValue) {
         titleValue = getTitle(displayValue);
       }
 
@@ -64,7 +65,7 @@ const SingleContent = React.forwardRef<HTMLInputElement, SharedContentProps>(
 
     // ========================== Render ==========================
     // Render value
-    const renderValue = displayValue ? (
+    const renderValue = hasDisplayValue ? (
       hasOptionStyle ? (
         <div
           className={clsx(`${prefixCls}-content-value`, optionClassName)}
@@ -88,7 +89,7 @@ const SingleContent = React.forwardRef<HTMLInputElement, SharedContentProps>(
       <div
         className={clsx(
           `${prefixCls}-content`,
-          displayValue && `${prefixCls}-content-has-value`,
+          hasDisplayValue && `${prefixCls}-content-has-value`,
           mergedSearchValue && `${prefixCls}-content-has-search-value`,
           hasOptionStyle && `${prefixCls}-content-has-option-style`,
           classNames?.content,

tests/placeholder.test.tsx

@@ -40,4 +40,11 @@ describe('Select placeholder', () => {
     });
     expect(container.querySelector('.rc-select-placeholder').textContent).toBe('placeholder');
   });
+
+  it('should have content-has-value class when value is empty string', () => {
+    const { container } = render(
+      <Select value="" placeholder="placeholder" options={[{ value: '', label: '' }]} />,
+    );
+    expect(container.querySelector('.rc-select-content-has-value')).toBeTruthy();
+  });
 });