[EuiFilterButton] Fix unstyled '0' content when numFilters is undefin…

…ed (#5268)

* [EuiFilterButton] Fix unstyled '0' content when numFilters is undefined

- showBadge was evaluating as '0' because numActiveFilters was evaluating as 0
- if numActiveFilters was 0 (0 && 0 > 0) validated as 0 :/ just JS things

* Add changelog entry

CHANGELOG.md

@@ -3,6 +3,7 @@
 **Bug fixes**
 
 - Fixed `SuperDatePicker` from crashing due to invalid time input ([#5263](https://github.com/elastic/eui/pull/5263))
+- Fixed content in `EuiFilterButton` again when `numFilters` is undefined ([#5268](https://github.com/elastic/eui/pull/5268))
 
 ## [`39.1.0`](https://github.com/elastic/eui/tree/v39.1.0)
 

src/components/filter_group/__snapshots__/filter_button.test.tsx.snap

@@ -217,3 +217,24 @@ exports[`EuiFilterButton renders zero properly 1`] = `
   </span>
 </button>
 `;
+
+exports[`EuiFilterButton does not render a badge or count if numFilters is not passed 1`] = `
+<button
+  aria-label="aria-label"
+  class="euiButtonEmpty euiButtonEmpty--text euiFilterButton testClass1 testClass2"
+  data-test-subj="test subject string"
+  type="button"
+>
+  <span
+    class="euiButtonContent euiButtonContent--iconRight euiButtonEmpty__content"
+  >
+    <span
+      class="euiButtonEmpty__text"
+    >
+      <span
+        class="euiFilterButton__textShift"
+      />
+    </span>
+  </span>
+</button>
+`;

src/components/filter_group/filter_button.test.tsx

@@ -21,7 +21,15 @@ describe('EuiFilterButton', () => {
 
   test('renders zero properly', () => {
     const component = render(
-      <EuiFilterButton {...requiredProps} numFilters={0} />
+      <EuiFilterButton {...requiredProps} numFilters={0} numActiveFilters={0} />
+    );
+
+    expect(component).toMatchSnapshot();
+  });
+
+  test('does not render a badge or count if numFilters is not passed', () => {
+    const component = render(
+      <EuiFilterButton {...requiredProps} numActiveFilters={0} />
     );
 
     expect(component).toMatchSnapshot();

src/components/filter_group/filter_button.tsx

@@ -68,7 +68,8 @@ export const EuiFilterButton: FunctionComponent<EuiFilterButtonProps> = ({
   ...rest
 }) => {
   const numFiltersDefined = numFilters != null; // != instead of !== to allow for null and undefined
-  const numActiveFiltersDefined = numActiveFilters && numActiveFilters > 0;
+  const numActiveFiltersDefined =
+    numActiveFilters != null && numActiveFilters > 0;
 
   const classes = classNames(
     'euiFilterButton',