Adjust uischema type guards to be compatible with 'strictNullChecks'

Author: sdirix

packages/core/src/models/uischema.ts

@@ -275,13 +275,13 @@ export const isLayout = (uischema: UISchemaElement): uischema is Layout =>
   (uischema as Layout).elements !== undefined;
 
 export const isScopable = (obj: unknown): obj is Scopable =>
-  obj && typeof obj === 'object';
+  !!obj && typeof obj === 'object';
 
 export const isScoped = (obj: unknown): obj is Scoped =>
   isScopable(obj) && typeof obj.scope === 'string';
 
 export const isLabelable = (obj: unknown): obj is Labelable =>
-  obj && typeof obj === 'object';
+  !!obj && typeof obj === 'object';
 
 export const isLabeled = <T = never>(obj: unknown): obj is Labeled<T> =>
   isLabelable(obj) && ['string', 'boolean'].includes(typeof obj.label);