fix(ui5-select): empty value string is ignored

[tw4]

Description

This PR ensures that <ui5-option value=""> options with an empty string value are correctly handled during form submission in the ui5-select component.

fixed #11736

Details

• Previously, options defined as <ui5-option value="">Empty</ui5-option> were not properly submitted with an empty string value.
• With this fix, options with an explicit empty string ("") as their value are now correctly included in the submitted form data.

Expected Behavior

• When the "Empty" option is selected, the submitted value should be an empty string ("").

• The result in the console or form data should look like:

  { select2: "" }

---

Screenshot

        <form onSubmit={(e) => this.handleSubmit(e)}>
          <ui5-select name="select2">
            <ui5-option value="value">Value</ui5-option>
            <ui5-option value="">Empty</ui5-option>
            <ui5-option>No Value Attribute</ui5-option>
          </ui5-select>
          <button type="submit">Submit</button>
        </form>

[nnaydenow]

Hi @dobrinyonkov , @PetyaMarkovaBogdanova,

Could you please take a look? Possible solution for: #11736