IntegrityException should be thrown for relational DBs only

framework/db/Command.php

@@ -781,12 +781,15 @@ class Command extends \yii\base\Component
             throw $e;
         } else {
             $exceptionClass = '\yii\db\Exception';
-            $errorMap = $this->db->getSchema()->errorMap;
-            foreach ($errorMap as $error => $class) {
+            $schema = $this->db->getSchema();
+            if ($schema instanceof Schema) {
+                $exceptionMap = $schema->exceptionMap;
+                foreach ($exceptionMap as $error => $class) {
                     if (strpos($e->getMessage(), $error) !== false) {
                         $exceptionClass = $class;
                     }
                 }
+            }
 
             $message = $e->getMessage()  . "\nThe SQL being executed was: $rawSql";
             $errorInfo = $e instanceof \PDOException ? $e->errorInfo : null;