Remove unneeded dependency

lib/ast-to-react.js

@@ -75,7 +75,6 @@
  */
 
 import React from 'react'
-import ReactIs from 'react-is'
 import {stringify as commas} from 'comma-separated-tokens'
 import {whitespace} from 'hast-util-whitespace'
 import {find, hastToReact, svg} from 'property-information'
@@ -185,14 +184,15 @@ function toReact(state, node, index, parent) {
   // Restore parent schema.
   state.schema = parentSchema
 
+  /** @type {ComponentType<any> | string} */
   const component =
     options.components && own.call(options.components, name)
-      ? options.components[name]
+      ? options.components[name] || name
       : name
   const basic = typeof component === 'string' || component === React.Fragment
 
-  if (!ReactIs.isValidElementType(component)) {
-    throw new TypeError(
+  if (!basic && typeof component !== 'function') {
+    throw new Error(
       `Component for name \`${name}\` not defined or is not renderable`
     )
   }

package.json

@@ -84,10 +84,9 @@
     "@types/unist": "^3.0.0",
     "comma-separated-tokens": "^2.0.0",
     "hast-util-whitespace": "^3.0.0",
-    "mdast-util-to-hast": "^13.0.2",
+    "mdast-util-to-hast": "^13.0.0",
     "prop-types": "^15.0.0",
     "property-information": "^6.0.0",
-    "react-is": "^18.0.0",
     "remark-parse": "^11.0.0",
     "remark-rehype": "^11.0.0",
     "space-separated-tokens": "^2.0.0",
@@ -105,7 +104,6 @@
     "@types/node": "^20.0.0",
     "@types/react": "^18.0.0",
     "@types/react-dom": "^18.0.0",
-    "@types/react-is": "^18.0.0",
     "c8": "^8.0.0",
     "esbuild": "^0.19.0",
     "eslint-plugin-es": "^4.0.0",

test/test.jsx

@@ -645,6 +645,22 @@ test('react-markdown', async function (t) {
     }, /Component for name `h1`/)
   })
 
+  await t.test('should support `null`, `undefined` in components', function () {
+    assert.equal(
+      asHtml(
+        <Markdown
+          children="# *a*"
+          components={{
+            // @ts-expect-error: code allows `null` but TS does not.
+            h1: null,
+            em: undefined
+          }}
+        />
+      ),
+      '<h1><em>a</em></h1>'
+    )
+  })
+
   await t.test('should support `components` (headings; `level`)', function () {
     let calls = 0