[TASK] Make Boolean tests explicit

config/phpstan-baseline.neon

@@ -1,11 +1,5 @@
 parameters:
 	ignoreErrors:
-		-
-			message: '#^Only booleans are allowed in an if condition, string given\.$#'
-			identifier: if.condNotBoolean
-			count: 1
-			path: ../src/CSSList/AtRuleBlockList.php
-
 		-
 			message: '#^Call to function is_string\(\) with Sabberworm\\CSS\\Parsing\\ParserState will always evaluate to false\.$#'
 			identifier: function.impossibleType
@@ -54,12 +48,6 @@ parameters:
 			count: 1
 			path: ../src/Parsing/ParserState.php
 
-		-
-			message: '#^Only booleans are allowed in an if condition, Sabberworm\\CSS\\Value\\RuleValueList\|string\|null given\.$#'
-			identifier: if.condNotBoolean
-			count: 1
-			path: ../src/Rule/Rule.php
-
 		-
 			message: '#^Parameters should have "string" types as the only types passed to this method$#'
 			identifier: typePerfect.narrowPublicClassMethodParamType

src/CSSList/AtRuleBlockList.php

@@ -55,7 +55,7 @@ public function render(OutputFormat $outputFormat): string
         $result = $formatter->comments($this);
         $result .= $outputFormat->getContentBeforeAtRuleBlock();
         $arguments = $this->arguments;
-        if ($arguments) {
+        if ($arguments !== '') {
             $arguments = ' ' . $arguments;
         }
         $result .= "@{$this->type}$arguments{$formatter->spaceBeforeOpeningBrace()}{";

src/Rule/Rule.php

@@ -158,7 +158,7 @@ public function addValue($value, string $type = ' '): void
         if (!($this->value instanceof RuleValueList) || $this->value->getListSeparator() !== $type) {
             $currentValue = $this->value;
             $this->value = new RuleValueList($type, $this->getLineNumber());
-            if ($currentValue) {
+            if ($currentValue !== null && $currentValue !== '') {
                 $this->value->addListComponent($currentValue);
             }
         }