Fix deepKeys to not throw on sparse arrays

Fixes #108

index.js

@@ -296,7 +296,8 @@ export function escapePath(path) {
 // The keys returned by Object.entries() for arrays are strings
 function entries(value) {
 	if (Array.isArray(value)) {
-		return value.map((value, index) => [index, value]);
+		// We use `[...value]` to convert sparse entries to normal ones.
+		return [...value].map((value, index) => [index, value]);
 	}
 
 	return Object.entries(value);

test.js

@@ -436,6 +436,7 @@ test('deepKeys', t => {
 			a: 0,
 		},
 	};
+
 	const keys = deepKeys(object);
 
 	t.deepEqual(keys, [
@@ -463,6 +464,20 @@ test('deepKeys', t => {
 	t.deepEqual(deepKeys(0), []);
 });
 
+test('deepKeys - does not throw on sparse array', t => {
+	const object = {
+		sparse: [1,,3], // eslint-disable-line no-sparse-arrays, comma-spacing
+	};
+
+	const keys = deepKeys(object);
+
+	t.deepEqual(keys, [
+		'sparse[0]',
+		'sparse[1]',
+		'sparse[2]',
+	]);
+});
+
 test('prevent setting/getting `__proto__`', t => {
 	setProperty({}, '__proto__.unicorn', '🦄');
 	t.not({}.unicorn, '🦄'); // eslint-disable-line no-use-extend-native/no-use-extend-native