Fix psalm issues

src/Console/Helper/ConfiguredLoader.php

@@ -23,7 +23,8 @@ public static function createFromConfig(?string $file, callable $configurator =
     {
         $loader = new StreamWrapperLoader();
 
-        if ($file) {
+        if ($file !== null) {
+            invariant($file !== '', 'File must not be empty.');
             invariant(Filesystem\exists($file), 'File "%s" does not exist.', $file);
             invariant(Filesystem\is_file($file), 'File "%s" is not a file.', $file);
             invariant(Filesystem\is_readable($file), 'File "%s" is not readable.', $file);
@@ -34,6 +35,6 @@ public static function createFromConfig(?string $file, callable $configurator =
             $loader = instance_of(WsdlLoader::class)->assert($included);
         }
 
-        return $configurator ? $configurator($loader) : $loader;
+        return $configurator !== null ? $configurator($loader) : $loader;
     }
 }

src/Xml/Configurator/FlattenWsdlImports.php

@@ -60,7 +60,7 @@ private function importWsdlImportElement(DOMElement $import): void
         );
 
         $result = $this->context->import($location);
-        if (!$result) {
+        if ($result === null || $result === '') {
             remove($import);
             return;
         }

src/Xml/Configurator/FlattenXsdImports.php

@@ -119,12 +119,6 @@ private function importSchema(DOMElement $import): ?DOMElement
             return null;
         }
 
-        // Normally an import has an owner document, since it is coming from xpath on an existing document
-        // However, static analysis does not know about this.
-        if (!$import->ownerDocument) {
-            return null;
-        }
-
         // Find the schema that wants to import the new schema:
         $doc = Document::fromUnsafeDocument($import->ownerDocument);
         $xpath = $doc->xpath(new WsdlPreset($doc));
@@ -158,7 +152,7 @@ private function loadSchema(string $location): ?DOMElement
         $path = IncludePathBuilder::build($location, $this->currentLocation);
         $result = $this->context->import($path);
 
-        if (!$result) {
+        if ($result === null || $result === '') {
             return null;
         }
 

src/Xml/Validator/SchemaSyntaxValidator.php

@@ -17,9 +17,12 @@ final class SchemaSyntaxValidator implements Validator
 {
     private string $xsd;
 
+    /**
+     * @param non-empty-string|null $xsd
+     */
     public function __construct(?string $xsd = null)
     {
-        $this->xsd = $xsd ?: dirname(__DIR__, 3).'/xsd/XMLSchema.xsd';
+        $this->xsd = $xsd ?? dirname(__DIR__, 3).'/xsd/XMLSchema.xsd';
     }
 
     /**

src/Xml/Validator/WsdlSyntaxValidator.php

@@ -15,9 +15,12 @@ final class WsdlSyntaxValidator implements Validator
 {
     private string $xsd;
 
+    /**
+     * @param non-empty-string|null $xsd
+     */
     public function __construct(?string $xsd = null)
     {
-        $this->xsd = $xsd ?: dirname(__DIR__, 3).'/xsd/wsdl.xsd';
+        $this->xsd = $xsd ?? dirname(__DIR__, 3).'/xsd/wsdl.xsd';
     }
 
     /**