Change Value Used in DB Plugin

Summary:
- Add value for null type to use `.value` easier
- Add value to string by directly converting to string if possible; otherwise null

Reviewed By: jknoxville

Differential Revision: D21788242

fbshipit-source-id: f3a9f995de6b4cb1b304981c8adaaba70105c988

desktop/app/src/index.tsx

@@ -91,7 +91,11 @@ export {
   default as ManagedTable_immutable,
   ManagedTableProps_immutable,
 } from './ui/components/table/ManagedTable_immutable';
-export {Value, renderValue} from './ui/components/table/TypeBasedValueRenderer';
+export {
+  Value,
+  renderValue,
+  valueToNullableString,
+} from './ui/components/table/TypeBasedValueRenderer';
 export {
   DataValueExtractor,
   DataInspectorExpanded,

desktop/app/src/ui/components/table/TypeBasedValueRenderer.tsx

@@ -27,6 +27,7 @@ export type Value =
     }
   | {
       type: 'null';
+      value: null;
     };
 
 const WrappingText = styled(Text)({
@@ -59,6 +60,10 @@ const BooleanValue = styled(NonWrappingText)<{active?: boolean}>((props) => ({
 }));
 BooleanValue.displayName = 'TypeBasedValueRenderer:BooleanValue';
 
+export function valueToNullableString(val: Value): string | null {
+  return val.value?.toString() ?? null;
+}
+
 export function renderValue(val: Value, wordWrap?: boolean) {
   const TextComponent = wordWrap ? WrappingText : NonWrappingText;
   switch (val.type) {