fix crash when passing a callable instead of a string to ->if() method

Author: milewski

src/ConditionalContainer.php

@@ -69,7 +69,7 @@ public function if($expression): self
         return $this;
     }
 
-    public function orIf(string $expression): self
+    public function orIf($expression): self
     {
         return $this->if($expression);
     }

src/HasConditionalContainer.php

@@ -103,7 +103,9 @@ public function availableFields(NovaRequest $request)
 
             $fields = parent::availableFields($request);
             $containers = $this->findAllContainers($fields);
-            $expressionsMap = $containers->flatMap->expressions;
+            $expressionsMap = $containers->flatMap->expressions->map(function ($expression) {
+                return is_callable($expression) ? $expression() : $expression;
+            });
 
             $cleanUpMethodName = $controller instanceof UpdateFieldController ?
                 'removeNonUpdateFields' :
@@ -141,7 +143,9 @@ public function availableFields(NovaRequest $request)
 
         $allFields = $this->fields($request);
         $containers = $this->findAllContainers($allFields);
-        $expressionsMap = $containers->flatMap->expressions;
+        $expressionsMap = $containers->flatMap->expressions->map(function ($expression) {
+            return is_callable($expression) ? $expression() : $expression;
+        });
 
         $fields = $this->flattenDependencies(
             $request, $this->preloadRelationships($expressionsMap, $allFields)