fix: null string passed as text to Flag component prevents page load (#466)

* Coerce null to empty string in Flag

Fixes bug where a null value passed as text to a Flag component breaks entire pages.

* added unit test

amundsen_application/static/js/components/common/Flag/index.tsx

@@ -16,6 +16,7 @@ export interface FlagProps {
 }
 
 export function convertText(str: string, caseType: string): string {
+  str = str || '';
   switch (caseType) {
     case CaseType.LOWER_CASE:
       return str.toLowerCase();

amundsen_application/static/js/components/common/Flag/tests/index.spec.tsx

@@ -51,5 +51,9 @@ describe('Flag', () => {
         it('returns text in defauilt case', () => {
             expect(convertText(text, 'not a valid options')).toEqual(text);
         });
+
+        it('returns empty strings for null values', () => {
+            expect(convertText(null, CaseType.SENTENCE_CASE)).toEqual('');
+        });
     });
 });