diff --git a/.travis.yml b/.travis.yml
index 3dbfb3888..bf56cf747 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,7 +3,7 @@ php:
     - 7.1
     - 7.2
     - 7.3
-    - 7.4snapshot
+    - 7.4
 
 before_install:
     # turn off XDebug
@@ -36,12 +36,9 @@ jobs:
 
 
         -   stage: Static Analysis (informative)
-            install:
-                # Install PHPStan
-                - travis_retry composer create-project phpstan/phpstan-shim temp/phpstan --no-progress
-                - travis_retry composer install --no-progress --prefer-dist
+            php: 7.4
             script:
-                - php temp/phpstan/phpstan.phar analyse --autoload-file vendor/autoload.php --level 5 --configuration tests/phpstan.neon src
+                - composer run-script phpstan
 
 
         -   stage: Code Coverage
@@ -55,7 +52,6 @@ jobs:
     allow_failures:
         -   stage: Static Analysis (informative)
         -   stage: Code Coverage
-        -   php: 7.4snapshot
 
 
 sudo: false
diff --git a/composer.json b/composer.json
index 9425fc5b4..2a1912e70 100644
--- a/composer.json
+++ b/composer.json
@@ -19,7 +19,8 @@
 	},
 	"require-dev": {
 		"nette/tester": "~2.0",
-		"tracy/tracy": "^2.3"
+		"tracy/tracy": "^2.3",
+		"phpstan/phpstan": "^0.12"
 	},
 	"suggest": {
 		"ext-iconv": "to use Strings::webalize() and toAscii()",
@@ -34,6 +35,10 @@
 		"classmap": ["src/"]
 	},
 	"minimum-stability": "dev",
+	"scripts": {
+		"phpstan": "phpstan analyse --level 5 --configuration tests/phpstan.neon src",
+		"tester": "tester tests -s"
+	},
 	"extra": {
 		"branch-alias": {
 			"dev-master": "3.0-dev"
diff --git a/readme.md b/readme.md
index 0de6f5223..b0a6e8fe5 100644
--- a/readme.md
+++ b/readme.md
@@ -38,4 +38,5 @@ The recommended way to install is via Composer:
 composer require nette/utils
 ```
 
-It requires PHP version 7.1 and supports PHP up to 7.3.
+- Nette Utils 3.0 is compatible with PHP 7.1 to 7.4
+- Nette Utils 2.5 is compatible with PHP 5.6 to 7.4
diff --git a/src/Iterators/CachingIterator.php b/src/Iterators/CachingIterator.php
index 2204e2354..c2393554e 100644
--- a/src/Iterators/CachingIterator.php
+++ b/src/Iterators/CachingIterator.php
@@ -41,11 +41,11 @@ public function __construct($iterator)
 			do {
 				$iterator = $iterator->getIterator();
 			} while ($iterator instanceof \IteratorAggregate);
+			assert($iterator instanceof \Iterator);
 
+		} elseif ($iterator instanceof \Iterator) {
 		} elseif ($iterator instanceof \Traversable) {
-			if (!$iterator instanceof \Iterator) {
-				$iterator = new \IteratorIterator($iterator);
-			}
+			$iterator = new \IteratorIterator($iterator);
 		} else {
 			throw new Nette\InvalidArgumentException(sprintf('Invalid argument passed to %s; array or Traversable expected, %s given.', __CLASS__, is_object($iterator) ? get_class($iterator) : gettype($iterator)));
 		}
diff --git a/src/Utils/Html.php b/src/Utils/Html.php
index 508adc9d2..0daccf026 100644
--- a/src/Utils/Html.php
+++ b/src/Utils/Html.php
@@ -16,13 +16,219 @@
 /**
  * HTML helper.
  *
- * <code>
- * $el = Html::el('a')->href($link)->setText('Nette');
- * $el->class = 'myclass';
- * echo $el;
+ * @property string|null $accept
+ * @property string|null $accesskey
+ * @property string|null $action
+ * @property string|null $align
+ * @property string|null $allow
+ * @property string|null $alt
+ * @property bool|null   $async
+ * @property string|null $autocapitalize
+ * @property string|null $autocomplete
+ * @property bool|null   $autofocus
+ * @property bool|null   $autoplay
+ * @property string|null $charset
+ * @property bool|null   $checked
+ * @property string|null $cite
+ * @property string|null $class
+ * @property int|null    $cols
+ * @property int|null    $colspan
+ * @property string|null $content
+ * @property bool|null   $contenteditable
+ * @property bool|null   $controls
+ * @property string|null $coords
+ * @property string|null $crossorigin
+ * @property string|null $data
+ * @property string|null $datetime
+ * @property string|null $decoding
+ * @property bool|null   $default
+ * @property bool|null   $defer
+ * @property string|null $dir
+ * @property string|null $dirname
+ * @property bool|null   $disabled
+ * @property bool|null   $download
+ * @property string|null $draggable
+ * @property string|null $dropzone
+ * @property string|null $enctype
+ * @property string|null $for
+ * @property string|null $form
+ * @property string|null $formaction
+ * @property string|null $formenctype
+ * @property string|null $formmethod
+ * @property bool|null   $formnovalidate
+ * @property string|null $formtarget
+ * @property string|null $headers
+ * @property int|null    $height
+ * @property bool|null   $hidden
+ * @property float|null  $high
+ * @property string|null $href
+ * @property string|null $hreflang
+ * @property string|null $id
+ * @property string|null $integrity
+ * @property string|null $inputmode
+ * @property bool|null   $ismap
+ * @property string|null $itemprop
+ * @property string|null $kind
+ * @property string|null $label
+ * @property string|null $lang
+ * @property string|null $list
+ * @property bool|null   $loop
+ * @property float|null  $low
+ * @property float|null  $max
+ * @property int|null    $maxlength
+ * @property int|null    $minlength
+ * @property string|null $media
+ * @property string|null $method
+ * @property float|null  $min
+ * @property bool|null   $multiple
+ * @property bool|null   $muted
+ * @property string|null $name
+ * @property bool|null   $novalidate
+ * @property bool|null   $open
+ * @property float|null  $optimum
+ * @property string|null $pattern
+ * @property string|null $ping
+ * @property string|null $placeholder
+ * @property string|null $poster
+ * @property string|null $preload
+ * @property string|null $radiogroup
+ * @property bool|null   $readonly
+ * @property string|null $rel
+ * @property bool|null   $required
+ * @property bool|null   $reversed
+ * @property int|null    $rows
+ * @property int|null    $rowspan
+ * @property string|null $sandbox
+ * @property string|null $scope
+ * @property bool|null   $selected
+ * @property string|null $shape
+ * @property int|null    $size
+ * @property string|null $sizes
+ * @property string|null $slot
+ * @property int|null    $span
+ * @property string|null $spellcheck
+ * @property string|null $src
+ * @property string|null $srcdoc
+ * @property string|null $srclang
+ * @property string|null $srcset
+ * @property int|null    $start
+ * @property float|null  $step
+ * @property string|null $style
+ * @property int|null    $tabindex
+ * @property string|null $target
+ * @property string|null $title
+ * @property string|null $translate
+ * @property string|null $type
+ * @property string|null $usemap
+ * @property string|null $value
+ * @property int|null    $width
+ * @property string|null $wrap
  *
- * echo $el->startTag(), $el->endTag();
- * </code>
+ * @method self accept(?string $val)
+ * @method self accesskey(?string $val, bool $state = null)
+ * @method self action(?string $val)
+ * @method self align(?string $val)
+ * @method self allow(?string $val, bool $state = null)
+ * @method self alt(?string $val)
+ * @method self async(?bool $val)
+ * @method self autocapitalize(?string $val)
+ * @method self autocomplete(?string $val)
+ * @method self autofocus(?bool $val)
+ * @method self autoplay(?bool $val)
+ * @method self charset(?string $val)
+ * @method self checked(?bool $val)
+ * @method self cite(?string $val)
+ * @method self class(?string $val, bool $state = null)
+ * @method self cols(?int $val)
+ * @method self colspan(?int $val)
+ * @method self content(?string $val)
+ * @method self contenteditable(?bool $val)
+ * @method self controls(?bool $val)
+ * @method self coords(?string $val)
+ * @method self crossorigin(?string $val)
+ * @method self datetime(?string $val)
+ * @method self decoding(?string $val)
+ * @method self default(?bool $val)
+ * @method self defer(?bool $val)
+ * @method self dir(?string $val)
+ * @method self dirname(?string $val)
+ * @method self disabled(?bool $val)
+ * @method self download(?bool $val)
+ * @method self draggable(?string $val)
+ * @method self dropzone(?string $val)
+ * @method self enctype(?string $val)
+ * @method self for(?string $val)
+ * @method self form(?string $val)
+ * @method self formaction(?string $val)
+ * @method self formenctype(?string $val)
+ * @method self formmethod(?string $val)
+ * @method self formnovalidate(?bool $val)
+ * @method self formtarget(?string $val)
+ * @method self headers(?string $val, bool $state = null)
+ * @method self height(?int $val)
+ * @method self hidden(?bool $val)
+ * @method self high(?float $val)
+ * @method self hreflang(?string $val)
+ * @method self id(?string $val)
+ * @method self integrity(?string $val)
+ * @method self inputmode(?string $val)
+ * @method self ismap(?bool $val)
+ * @method self itemprop(?string $val)
+ * @method self kind(?string $val)
+ * @method self label(?string $val)
+ * @method self lang(?string $val)
+ * @method self list(?string $val)
+ * @method self loop(?bool $val)
+ * @method self low(?float $val)
+ * @method self max(?float $val)
+ * @method self maxlength(?int $val)
+ * @method self minlength(?int $val)
+ * @method self media(?string $val)
+ * @method self method(?string $val)
+ * @method self min(?float $val)
+ * @method self multiple(?bool $val)
+ * @method self muted(?bool $val)
+ * @method self name(?string $val)
+ * @method self novalidate(?bool $val)
+ * @method self open(?bool $val)
+ * @method self optimum(?float $val)
+ * @method self pattern(?string $val)
+ * @method self ping(?string $val, bool $state = null)
+ * @method self placeholder(?string $val)
+ * @method self poster(?string $val)
+ * @method self preload(?string $val)
+ * @method self radiogroup(?string $val)
+ * @method self readonly(?bool $val)
+ * @method self rel(?string $val)
+ * @method self required(?bool $val)
+ * @method self reversed(?bool $val)
+ * @method self rows(?int $val)
+ * @method self rowspan(?int $val)
+ * @method self sandbox(?string $val, bool $state = null)
+ * @method self scope(?string $val)
+ * @method self selected(?bool $val)
+ * @method self shape(?string $val)
+ * @method self size(?int $val)
+ * @method self sizes(?string $val)
+ * @method self slot(?string $val)
+ * @method self span(?int $val)
+ * @method self spellcheck(?string $val)
+ * @method self src(?string $val)
+ * @method self srcdoc(?string $val)
+ * @method self srclang(?string $val)
+ * @method self srcset(?string $val)
+ * @method self start(?int $val)
+ * @method self step(?float $val)
+ * @method self style(?string $property, string $val = null)
+ * @method self tabindex(?int $val)
+ * @method self target(?string $val)
+ * @method self title(?string $val)
+ * @method self translate(?string $val)
+ * @method self type(?string $val)
+ * @method self usemap(?string $val)
+ * @method self value(?string $val)
+ * @method self width(?int $val)
+ * @method self wrap(?string $val)
  */
 class Html implements \ArrayAccess, \Countable, \IteratorAggregate, IHtmlString
 {
diff --git a/src/Utils/Image.php b/src/Utils/Image.php
index c9fb5e12f..bad03c391 100644
--- a/src/Utils/Image.php
+++ b/src/Utils/Image.php
@@ -62,19 +62,23 @@
  * @method void flip(int $mode)
  * @method array ftText($size, $angle, $x, $y, $col, string $fontFile, string $text, array $extrainfo = null)
  * @method void gammaCorrect(float $inputgamma, float $outputgamma)
+ * @method array getClip()
  * @method int interlace($interlace = null)
  * @method bool isTrueColor()
  * @method void layerEffect($effect)
  * @method void line($x1, $y1, $x2, $y2, $color)
+ * @method void openPolygon(array $points, int $num_points, int $color)
  * @method void paletteCopy(Image $source)
  * @method void paletteToTrueColor()
  * @method void polygon(array $points, $numPoints, $color)
  * @method array psText(string $text, $font, $size, $color, $backgroundColor, $x, $y, $space = null, $tightness = null, float $angle = null, $antialiasSteps = null)
  * @method void rectangle($x1, $y1, $x2, $y2, $col)
+ * @method mixed resolution(int $res_x = null, int $res_y = null)
  * @method Image rotate(float $angle, $backgroundColor)
  * @method void saveAlpha(bool $saveflag)
  * @method Image scale(int $newWidth, int $newHeight = -1, int $mode = IMG_BILINEAR_FIXED)
  * @method void setBrush(Image $brush)
+ * @method void setClip(int $x1, int $y1, int $x2, int $y2)
  * @method void setPixel($x, $y, $color)
  * @method void setStyle(array $style)
  * @method void setThickness($thickness)
@@ -262,8 +266,8 @@ public function getImageResource()
 
 	/**
 	 * Resizes image.
-	 * @param  int|string  $width in pixels or percent
-	 * @param  int|string  $height in pixels or percent
+	 * @param  int|string|null  $width in pixels or percent
+	 * @param  int|string|null  $height in pixels or percent
 	 * @return static
 	 */
 	public function resize($width, $height, int $flags = self::FIT)
@@ -293,20 +297,20 @@ public function resize($width, $height, int $flags = self::FIT)
 
 	/**
 	 * Calculates dimensions of resized image.
-	 * @param  int|string  $newWidth in pixels or percent
-	 * @param  int|string  $newHeight in pixels or percent
+	 * @param  int|string|null  $newWidth in pixels or percent
+	 * @param  int|string|null  $newHeight in pixels or percent
 	 */
 	public static function calculateSize(int $srcWidth, int $srcHeight, $newWidth, $newHeight, int $flags = self::FIT): array
 	{
 		if (is_string($newWidth) && substr($newWidth, -1) === '%') {
-			$newWidth = (int) round($srcWidth / 100 * abs(substr($newWidth, 0, -1)));
+			$newWidth = (int) round($srcWidth / 100 * abs((int) substr($newWidth, 0, -1)));
 			$percents = true;
 		} else {
 			$newWidth = (int) abs($newWidth);
 		}
 
 		if (is_string($newHeight) && substr($newHeight, -1) === '%') {
-			$newHeight = (int) round($srcHeight / 100 * abs(substr($newHeight, 0, -1)));
+			$newHeight = (int) round($srcHeight / 100 * abs((int) substr($newHeight, 0, -1)));
 			$flags |= empty($percents) ? 0 : self::STRETCH;
 		} else {
 			$newHeight = (int) abs($newHeight);
@@ -381,16 +385,16 @@ public function crop($left, $top, $width, $height)
 	public static function calculateCutout(int $srcWidth, int $srcHeight, $left, $top, $newWidth, $newHeight): array
 	{
 		if (is_string($newWidth) && substr($newWidth, -1) === '%') {
-			$newWidth = (int) round($srcWidth / 100 * substr($newWidth, 0, -1));
+			$newWidth = (int) round($srcWidth / 100 * (int) substr($newWidth, 0, -1));
 		}
 		if (is_string($newHeight) && substr($newHeight, -1) === '%') {
-			$newHeight = (int) round($srcHeight / 100 * substr($newHeight, 0, -1));
+			$newHeight = (int) round($srcHeight / 100 * (int) substr($newHeight, 0, -1));
 		}
 		if (is_string($left) && substr($left, -1) === '%') {
-			$left = (int) round(($srcWidth - $newWidth) / 100 * substr($left, 0, -1));
+			$left = (int) round(($srcWidth - $newWidth) / 100 * (int) substr($left, 0, -1));
 		}
 		if (is_string($top) && substr($top, -1) === '%') {
-			$top = (int) round(($srcHeight - $newHeight) / 100 * substr($top, 0, -1));
+			$top = (int) round(($srcHeight - $newHeight) / 100 * (int) substr($top, 0, -1));
 		}
 		if ($left < 0) {
 			$newWidth += $left;
@@ -439,11 +443,11 @@ public function place(self $image, $left = 0, $top = 0, int $opacity = 100)
 		$height = $image->getHeight();
 
 		if (is_string($left) && substr($left, -1) === '%') {
-			$left = (int) round(($this->getWidth() - $width) / 100 * substr($left, 0, -1));
+			$left = (int) round(($this->getWidth() - $width) / 100 * (int) substr($left, 0, -1));
 		}
 
 		if (is_string($top) && substr($top, -1) === '%') {
-			$top = (int) round(($this->getHeight() - $height) / 100 * substr($top, 0, -1));
+			$top = (int) round(($this->getHeight() - $height) / 100 * (int) substr($top, 0, -1));
 		}
 
 		$output = $input = $image->image;
@@ -548,21 +552,21 @@ private function output(int $type, ?int $quality, string $file = null): void
 		switch ($type) {
 			case self::JPEG:
 				$quality = $quality === null ? 85 : max(0, min(100, $quality));
-				$success = imagejpeg($this->image, $file, $quality);
+				$success = @imagejpeg($this->image, $file, $quality); // @ is escalated to exception
 				break;
 
 			case self::PNG:
 				$quality = $quality === null ? 9 : max(0, min(9, $quality));
-				$success = imagepng($this->image, $file, $quality);
+				$success = @imagepng($this->image, $file, $quality); // @ is escalated to exception
 				break;
 
 			case self::GIF:
-				$success = imagegif($this->image, $file);
+				$success = @imagegif($this->image, $file); // @ is escalated to exception
 				break;
 
 			case self::WEBP:
 				$quality = $quality === null ? 80 : max(0, min(100, $quality));
-				$success = imagewebp($this->image, $file, $quality);
+				$success = @imagewebp($this->image, $file, $quality); // @ is escalated to exception
 				break;
 
 			default:
diff --git a/src/Utils/Strings.php b/src/Utils/Strings.php
index 234ff5ab5..74a34c1f9 100644
--- a/src/Utils/Strings.php
+++ b/src/Utils/Strings.php
@@ -104,8 +104,8 @@ public static function substring(string $s, int $start, int $length = null): str
 	public static function normalize(string $s): string
 	{
 		// convert to compressed normal form (NFC)
-		if (class_exists('Normalizer', false)) {
-			$s = \Normalizer::normalize($s, \Normalizer::FORM_C);
+		if (class_exists('Normalizer', false) && ($n = \Normalizer::normalize($s, \Normalizer::FORM_C)) !== false) {
+			$s = $n;
 		}
 
 		$s = self::normalizeNewLines($s);
diff --git a/tests/phpstan.neon b/tests/phpstan.neon
index 0ce67d66a..12dc61b3f 100644
--- a/tests/phpstan.neon
+++ b/tests/phpstan.neon
@@ -1,5 +1,5 @@
 parameters:
-	bootstrap: tests/phpstan-bootstrap.php
+	bootstrap: phpstan-bootstrap.php
 
 	ignoreErrors:
 		# PHPStan does not support dynamic by reference return used by Nette\Utils\Strings::pcre()
@@ -7,6 +7,3 @@ parameters:
 
 		# PHPStan does not support RecursiveIteratorIterator proxying unknown method calls to inner iterator
 		- '#RecursiveIteratorIterator::getSubPathName\(\)#'
-
-		# PHPStan does not support comparing null
-		- '#Nette\\Utils\\Strings::substring\(\) expects int, int\|null given#'