diff --git a/lib/Doctrine/DBAL/Schema/Comparator.php b/lib/Doctrine/DBAL/Schema/Comparator.php
index 03b800e396d..16582f7a79e 100644
--- a/lib/Doctrine/DBAL/Schema/Comparator.php
+++ b/lib/Doctrine/DBAL/Schema/Comparator.php
@@ -12,6 +12,7 @@
 use function array_unique;
 use function assert;
 use function count;
+use function strcasecmp;
 use function strtolower;
 
 /**
@@ -259,7 +260,10 @@ public function diffTable(Table $table1, Table $table2)
                 if ($this->diffForeignKey($constraint1, $constraint2) === false) {
                     unset($fromFkeys[$key1], $toFkeys[$key2]);
                 } else {
-                    if (strtolower($constraint1->getName()) === strtolower($constraint2->getName())) {
+                    $name1 = $constraint1->getName();
+                    $name2 = $constraint2->getName();
+
+                    if ($name1 !== null && $name2 !== null && strcasecmp($name1, $name2) === 0) {
                         $tableDifferences->changedForeignKeys[] = $constraint2;
                         $changes++;
                         unset($fromFkeys[$key1], $toFkeys[$key2]);
@@ -349,8 +353,20 @@ private function detectIndexRenamings(TableDiff $tableDifferences) : void
 
             [$removedIndex, $addedIndex] = $candidateIndexes[0];
 
-            $removedIndexName = strtolower($removedIndex->getName());
-            $addedIndexName   = strtolower($addedIndex->getName());
+            $removedIndexName = $removedIndex->getName();
+
+            if ($removedIndexName === null) {
+                continue;
+            }
+
+            $addedIndexName = $addedIndex->getName();
+
+            if ($addedIndexName === null) {
+                continue;
+            }
+
+            $removedIndexName = strtolower($removedIndexName);
+            $addedIndexName   = strtolower($addedIndexName);
 
             if (isset($tableDifferences->renamedIndexes[$removedIndexName])) {
                 continue;
diff --git a/lib/Doctrine/DBAL/Schema/SchemaException.php b/lib/Doctrine/DBAL/Schema/SchemaException.php
index 72c38870f12..cd0fa483c3d 100644
--- a/lib/Doctrine/DBAL/Schema/SchemaException.php
+++ b/lib/Doctrine/DBAL/Schema/SchemaException.php
@@ -116,6 +116,17 @@ public static function namedForeignKeyRequired(Table $localTable, ForeignKeyCons
         );
     }
 
+    public static function namedIndexRequired(Table $table, Index $index) : self
+    {
+        return new self(
+            sprintf(
+                'The performed schema operation on %s requires a named index, but the given index on (%s) is currently unnamed.',
+                $table->getName(),
+                implode(', ', $index->getColumns())
+            )
+        );
+    }
+
     public static function alterTableChangeNotSupported(string $changeName) : self
     {
         return new self(
diff --git a/lib/Doctrine/DBAL/Schema/Visitor/RemoveNamespacedAssets.php b/lib/Doctrine/DBAL/Schema/Visitor/RemoveNamespacedAssets.php
index 8f3a2a822ef..d36947a55cf 100644
--- a/lib/Doctrine/DBAL/Schema/Visitor/RemoveNamespacedAssets.php
+++ b/lib/Doctrine/DBAL/Schema/Visitor/RemoveNamespacedAssets.php
@@ -4,6 +4,7 @@
 
 use Doctrine\DBAL\Schema\ForeignKeyConstraint;
 use Doctrine\DBAL\Schema\Schema;
+use Doctrine\DBAL\Schema\SchemaException;
 use Doctrine\DBAL\Schema\Sequence;
 use Doctrine\DBAL\Schema\Table;
 
@@ -57,6 +58,8 @@ public function acceptSequence(Sequence $sequence) : void
 
     /**
      * {@inheritdoc}
+     *
+     * @throws SchemaException
      */
     public function acceptForeignKey(Table $localTable, ForeignKeyConstraint $fkConstraint) : void
     {
@@ -64,7 +67,8 @@ public function acceptForeignKey(Table $localTable, ForeignKeyConstraint $fkCons
         // RemoveNamespacedAssets#acceptTable call. Removing Foreign keys that
         // point to nowhere.
         if (! $this->schema->hasTable($fkConstraint->getForeignTableName())) {
-            $localTable->removeForeignKey($fkConstraint->getName());
+            $this->removeForeignKey($localTable, $fkConstraint);
+
             return;
         }
 
@@ -73,6 +77,20 @@ public function acceptForeignKey(Table $localTable, ForeignKeyConstraint $fkCons
             return;
         }
 
-        $localTable->removeForeignKey($fkConstraint->getName());
+        $this->removeForeignKey($localTable, $fkConstraint);
+    }
+
+    /**
+     * @throws SchemaException
+     */
+    private function removeForeignKey(Table $table, ForeignKeyConstraint $constraint) : void
+    {
+        $name = $constraint->getName();
+
+        if ($name === null) {
+            throw SchemaException::namedForeignKeyRequired($table, $constraint);
+        }
+
+        $table->removeForeignKey($name);
     }
 }
diff --git a/lib/Doctrine/DBAL/Sharding/SQLAzure/Schema/MultiTenantVisitor.php b/lib/Doctrine/DBAL/Sharding/SQLAzure/Schema/MultiTenantVisitor.php
index aaeb3060e4b..069ae52e9b1 100644
--- a/lib/Doctrine/DBAL/Sharding/SQLAzure/Schema/MultiTenantVisitor.php
+++ b/lib/Doctrine/DBAL/Sharding/SQLAzure/Schema/MultiTenantVisitor.php
@@ -6,6 +6,7 @@
 use Doctrine\DBAL\Schema\ForeignKeyConstraint;
 use Doctrine\DBAL\Schema\Index;
 use Doctrine\DBAL\Schema\Schema;
+use Doctrine\DBAL\Schema\SchemaException;
 use Doctrine\DBAL\Schema\Sequence;
 use Doctrine\DBAL\Schema\Table;
 use Doctrine\DBAL\Schema\Visitor\Visitor;
@@ -62,6 +63,8 @@ public function __construct(array $excludedTables = [], string $tenantColumnName
 
     /**
      * {@inheritdoc}
+     *
+     * @throws SchemaException
      */
     public function acceptTable(Table $table) : void
     {
@@ -82,9 +85,15 @@ public function acceptTable(Table $table) : void
             $table->dropPrimaryKey();
             $table->setPrimaryKey($indexColumns);
         } else {
-            $table->dropIndex($clusteredIndex->getName());
-            $table->addIndex($indexColumns, $clusteredIndex->getName());
-            $table->getIndex($clusteredIndex->getName())->addFlag('clustered');
+            $name = $clusteredIndex->getName();
+
+            if ($name === null) {
+                throw SchemaException::namedIndexRequired($table, $clusteredIndex);
+            }
+
+            $table->dropIndex($name);
+            $table->addIndex($indexColumns, $name);
+            $table->getIndex($name)->addFlag('clustered');
         }
     }