add nullable types functions

index.ts

@@ -1,5 +1,6 @@
 export * from './json/index.js'
 export * from './lazy/index.js'
 export * from './locale/index.js'
+export * from './nullables/index.js'
 export * from './raise/index.js'
 export * from './records/index.js'

nullables/index.ts

@@ -0,0 +1,11 @@
+/**
+ * Checks whenever a value is not nullable; same as value != null
+ *
+ * Useful for Array.filter():
+ *   const arr: (string | undefined)[] = [...]
+ *   ❌ arr.filter(v => v != null) // type: (string | undefined)[]
+ *   ❌ arr.filter(v => typeof v === 'string') // type: (string | undefined)[]
+ *   ✅ arr.filter(isNonNullable) // type: string[]
+ */
+export const isNonNullable = <T>(value: NonNullable<T> | undefined | null): value is NonNullable<T> =>
+  value != null