Fix clearable bug for single-option dropdowns.

Author: Shammamah Hossain

src/fragments/Dropdown.react.js

@@ -75,15 +75,15 @@ export default class Dropdown extends Component {
                     onChange={selectedOption => {
                         if (multi) {
                             let value;
-                            if (isNil(selectedOption)) {
+                            if (isNil(selectedOption) && this.props.clearable) {
                                 value = [];
                             } else {
                                 value = pluck('value', selectedOption);
                             }
                             setProps({value});
                         } else {
                             let value;
-                            if (isNil(selectedOption)) {
+                            if (isNil(selectedOption) && this.props.clearable) {
                                 value = null;
                             } else {
                                 value = selectedOption.value;

tests/integration/dropdown/test_clearable_false.py

@@ -0,0 +1,41 @@
+import dash
+from dash.dependencies import Input, Output
+import dash_core_components as dcc
+import dash_html_components as html
+
+from selenium.webdriver.common.keys import Keys
+
+
+def test_ddcf001_clearable_false_single(dash_duo):
+    app = dash.Dash(__name__)
+    app.layout = html.Div([
+        dcc.Dropdown(
+            id='my-unclearable-dropdown',
+            options=[
+                {'label': 'New York City', 'value': 'NYC'},
+                {'label': 'Montreal', 'value': 'MTL'},
+                {'label': 'San Francisco', 'value': 'SF'},
+            ],
+            value='MTL',
+            clearable=False
+        ),
+        html.Div(
+            id='dropdown-value',
+            style={'height': '10px', 'width': '10px'}
+        )
+    ])
+
+    @app.callback(
+        Output('dropdown-value', 'children'),
+        [Input('my-unclearable-dropdown', 'value')]
+    )
+    def update_value(val):
+        return val
+
+    dash_duo.start_server(app)
+
+    dropdown = dash_duo.find_element('#my-unclearable-dropdown input')
+    dropdown.send_keys(Keys.BACKSPACE)
+    dash_duo.find_element('#dropdown-value').click()
+
+    assert len(dash_duo.find_element('#dropdown-value').text) > 0