diff --git a/src/Composer/DependencyResolver/GenericRule.php b/src/Composer/DependencyResolver/GenericRule.php
index c86aa19cb..ab010db0e 100644
--- a/src/Composer/DependencyResolver/GenericRule.php
+++ b/src/Composer/DependencyResolver/GenericRule.php
@@ -77,7 +77,7 @@ class GenericRule extends Rule
      *
      * @return string
      */
-    public function __toString()
+    public function __toString(): string
     {
         $result = $this->isDisabled() ? 'disabled(' : '(';
 
diff --git a/src/Composer/DependencyResolver/MultiConflictRule.php b/src/Composer/DependencyResolver/MultiConflictRule.php
index a7fcb0036..104d578a8 100644
--- a/src/Composer/DependencyResolver/MultiConflictRule.php
+++ b/src/Composer/DependencyResolver/MultiConflictRule.php
@@ -96,7 +96,7 @@ class MultiConflictRule extends Rule
      *
      * @return string
      */
-    public function __toString()
+    public function __toString(): string
     {
         // TODO multi conflict?
         $result = $this->isDisabled() ? 'disabled(multi(' : '(multi(';
diff --git a/src/Composer/DependencyResolver/Rule2Literals.php b/src/Composer/DependencyResolver/Rule2Literals.php
index cbb40b220..9545686c8 100644
--- a/src/Composer/DependencyResolver/Rule2Literals.php
+++ b/src/Composer/DependencyResolver/Rule2Literals.php
@@ -108,7 +108,7 @@ class Rule2Literals extends Rule
      *
      * @return string
      */
-    public function __toString()
+    public function __toString(): string
     {
         $result = $this->isDisabled() ? 'disabled(' : '(';
 
diff --git a/src/Composer/Package/Link.php b/src/Composer/Package/Link.php
index 75f744bd1..a7628a720 100644
--- a/src/Composer/Package/Link.php
+++ b/src/Composer/Package/Link.php
@@ -150,7 +150,7 @@ class Link
     /**
      * @return string
      */
-    public function __toString()
+    public function __toString(): string
     {
         return $this->source.' '.$this->description.' '.$this->target.' ('.$this->constraint.')';
     }
diff --git a/src/Composer/Repository/PlatformRepository.php b/src/Composer/Repository/PlatformRepository.php
index 4952d234c..461191e4a 100644
--- a/src/Composer/Repository/PlatformRepository.php
+++ b/src/Composer/Repository/PlatformRepository.php
@@ -327,8 +327,8 @@ class PlatformRepository extends ArrayRepository
                     }
 
                     // ICU TZData version => 2019c
-                    if (Preg::isMatch('/^ICU TZData version => (?<version>.*)$/im', $info, $zoneinfoMatches)) {
-                        $this->addLibrary('icu-zoneinfo', Version::parseZoneinfoVersion($zoneinfoMatches['version']), 'zoneinfo ("Olson") database for icu');
+                    if (Preg::isMatch('/^ICU TZData version => (?<version>.*)$/im', $info, $zoneinfoMatches) && null !== ($version = Version::parseZoneinfoVersion($zoneinfoMatches['version']))) {
+                        $this->addLibrary('icu-zoneinfo', $version, 'zoneinfo ("Olson") database for icu');
                     }
 
                     // Add a separate version for the CLDR library version