A null inputstream should return an empty doc

Fixes #2252

src/main/java/org/jsoup/Jsoup.java

@@ -261,7 +261,7 @@ public static Document parse(Path path, @Nullable String charsetName, String bas
      @param baseUri     The URL where the HTML was retrieved from, to resolve relative links against.
      @return sane HTML
 
-     @throws IOException if the file could not be found, or read, or if the charsetName is invalid.
+     @throws IOException if the stream could not be read, or if the charsetName is invalid.
      */
     public static Document parse(InputStream in, @Nullable String charsetName, String baseUri) throws IOException {
         return DataUtil.load(in, charsetName, baseUri);
@@ -278,7 +278,7 @@ public static Document parse(InputStream in, @Nullable String charsetName, Strin
      @param parser alternate {@link Parser#xmlParser() parser} to use.
      @return sane HTML
 
-     @throws IOException if the file could not be found, or read, or if the charsetName is invalid.
+     @throws IOException if the stream could not be read, or if the charsetName is invalid.
      */
     public static Document parse(InputStream in, @Nullable String charsetName, String baseUri, Parser parser) throws IOException {
         return DataUtil.load(in, charsetName, baseUri, parser);

src/main/java/org/jsoup/internal/ControllableInputStream.java

@@ -46,11 +46,11 @@ private ControllableInputStream(SimpleBufferedInput in, int maxSize) {
 
     /**
      * If this InputStream is not already a ControllableInputStream, let it be one.
-     * @param in the input stream to (maybe) wrap
+     * @param in the input stream to (maybe) wrap. A {@code null} input will create an empty wrapped stream.
      * @param maxSize the maximum size to allow to be read. 0 == infinite.
      * @return a controllable input stream
      */
-    public static ControllableInputStream wrap(InputStream in, int maxSize) {
+    public static ControllableInputStream wrap(@Nullable InputStream in, int maxSize) {
         // bufferSize currently unused; consider implementing as a min size in the SoftPool recycler
         if (in instanceof ControllableInputStream)
             return (ControllableInputStream) in;

src/main/java/org/jsoup/internal/SimpleBufferedInput.java

@@ -24,8 +24,9 @@ class SimpleBufferedInput extends FilterInputStream {
     private int bufMark = -1;
     private boolean inReadFully = false; // true when the underlying inputstream has been read fully
 
-    SimpleBufferedInput(InputStream in) {
+    SimpleBufferedInput(@Nullable InputStream in) {
         super(in);
+        if (in == null) inReadFully = true; // effectively an empty stream
     }
 
     @Override
@@ -148,7 +149,7 @@ public void reset() throws IOException {
 
     @Override
     public void close() throws IOException {
-        super.close();
+        if (in != null) super.close();
         if (byteBuf == null) return; // already closed, or never allocated
         BufferPool.release(byteBuf); // return the buffer to the pool
         byteBuf = null; // NPE further attempts to read

src/test/java/org/jsoup/helper/DataUtilTest.java

@@ -337,4 +337,11 @@ void handlesUnlimitedRead() throws IOException {
 
         assertEquals(input, read);
     }
+
+    @Test void controllableInputStreamAllowsNull() throws IOException {
+        ControllableInputStream is = ControllableInputStream.wrap(null, 0);
+        assertNotNull(is);
+        assertTrue(is.baseReadFully());
+        is.close();
+    }
 }

src/test/java/org/jsoup/parser/HtmlParserTest.java

@@ -15,6 +15,7 @@
 import java.io.ByteArrayInputStream;
 import java.io.File;
 import java.io.IOException;
+import java.io.InputStream;
 import java.util.List;
 import java.util.stream.Stream;
 
@@ -1962,4 +1963,13 @@ private static void assertMathNamespace(Element el) {
         assertEquals("hidden", div.attr("id"));
         assertNotNull(div.attribute("--"));
     }
+
+    @Test void nullStreamReturnsEmptyDoc() throws IOException {
+        // https://github.com/jhy/jsoup/issues/2252
+        InputStream stream = null;
+        Document doc = Jsoup.parse(stream, null, "");
+        // don't want to mark parse(stream) as @Nullable, as it's more useful to show the warning. But support it, for backwards compat
+        assertNotNull(doc);
+        assertEquals("", doc.title());
+    }
 }