Make Buffer::read() consistent with other InputStreams, returning "" …

…at EOF

src/main/php/io/streams/Buffer.class.php

@@ -95,21 +95,17 @@ public function available() {
    * Read a string
    *
    * @param  int $limit
-   * @return ?string
+   * @return string
    */
   public function read($limit= 8192) {
     if ($this->file) {
       $this->draining || $this->file->seek(0, SEEK_SET) && $this->draining= true;
-      $chunk= $this->file->read($limit);
-      return false === $chunk ? null : $chunk;
-    } else if ($this->pointer < $this->size) {
+      return (string)$this->file->read($limit);
+    } else {
       $this->draining= true;
       $chunk= substr($this->memory, $this->pointer, $limit);
       $this->pointer+= strlen($chunk);
       return $chunk;
-    } else {
-      $this->draining= true;
-      return null;
     }
   }
 

src/test/php/io/unittest/BufferTest.class.php

@@ -58,7 +58,7 @@ public function read_after_eof($length) {
     Assert::equals($length, $fixture->available());
     Assert::equals($bytes, $fixture->read());
     Assert::equals(0, $fixture->available());
-    Assert::equals(null, $fixture->read());
+    Assert::equals('', $fixture->read());
   }
 
   #[Test, Values([127, 128, 129])]