diff --git a/mlir/include/mlir/IR/AttrTypeBase.td b/mlir/include/mlir/IR/AttrTypeBase.td
--- a/mlir/include/mlir/IR/AttrTypeBase.td
+++ b/mlir/include/mlir/IR/AttrTypeBase.td
@@ -329,6 +329,18 @@
 class TypeParameter<string type, string desc, string accessorType = "">
  : AttrOrTypeParameter<type, desc, accessorType>;
 
+// An optional parameter.
+class OptionalParameter<string type, string desc = ""> :
+    AttrOrTypeParameter<type, desc> {
+  let defaultValue = cppStorageType # "()";
+}
+
+// A parameter with a default value.
+class DefaultValuedParameter<string type, string value, string desc = ""> :
+    AttrOrTypeParameter<type, desc> {
+  let defaultValue = value;
+}
+
 // For StringRefs, which require allocation.
 class StringRefParameter<string desc = ""> :
     AttrOrTypeParameter<"::llvm::StringRef", desc> {
@@ -350,6 +362,15 @@
   let cppStorageType = "::llvm::SmallVector<" # arrayOf # ">";
 }
 
+// Regular array parameters cannot be parsed when empty. This optional array
+// parameter can be used with optional groups to be parsed when empty.
+class OptionalArrayRefParameter<string arrayOf, string desc = ""> :
+    OptionalParameter<"::llvm::ArrayRef<" # arrayOf # ">", desc> {
+  let allocator = [{$_dst = $_allocator.copyInto($_self);}];
+  let cppStorageType = "::llvm::SmallVector<" # arrayOf # ">";
+  let comparator = "::llvm::makeArrayRef($_lhs) == ::llvm::makeArrayRef($_rhs)";
+}
+
 // For classes which require allocation and have their own allocateInto method.
 class SelfAllocationParameter<string type, string desc> :
     AttrOrTypeParameter<type, desc> {
@@ -367,18 +388,6 @@
   }];
 }
 
-// An optional parameter.
-class OptionalParameter<string type, string desc = ""> :
-    AttrOrTypeParameter<type, desc> {
-  let defaultValue = cppStorageType # "()";
-}
-
-// A parameter with a default value.
-class DefaultValuedParameter<string type, string value, string desc = ""> :
-    AttrOrTypeParameter<type, desc> {
-  let defaultValue = value;
-}
-
 // This is a special attribute parameter that represents the "self" type of the
 // attribute. It is specially handled by the assembly format generator to derive
 // its value from the optional trailing type after each attribute.
@@ -406,9 +415,9 @@
 class ArrayOfAttr<Dialect dialect, string attrName, string attrMnemonic,
                   string eltName, list<Trait> traits = []>
     : AttrDef<dialect, attrName, traits> {
-  let parameters = (ins ArrayRefParameter<eltName>:$value);
+  let parameters = (ins OptionalArrayRefParameter<eltName>:$value);
   let mnemonic = attrMnemonic;
-  let assemblyFormat = "`[` $value `]`";
+  let assemblyFormat = "`[` (`]`) : ($value^ `]`)?";
 
   let returnType = "::llvm::ArrayRef<" # eltName # ">";
   let constBuilderCall = "$_builder.getAttr<" # attrName # "Attr>($0)";
diff --git a/mlir/test/IR/array-of-attr.mlir b/mlir/test/IR/array-of-attr.mlir
--- a/mlir/test/IR/array-of-attr.mlir
+++ b/mlir/test/IR/array-of-attr.mlir
@@ -8,3 +8,7 @@
     b = [0, 1, -42, 42],
     // CHECK-SAME: [a, b, b, a]
     c = [a, b, b, a]
+
+// CHECK: test.array_of_attr_op
+// CHECK-SAME: a = [], b = [], c = []
+test.array_of_attr_op a = [], b = [], c = []
diff --git a/mlir/test/lib/Dialect/Test/TestAttrDefs.td b/mlir/test/lib/Dialect/Test/TestAttrDefs.td
--- a/mlir/test/lib/Dialect/Test/TestAttrDefs.td
+++ b/mlir/test/lib/Dialect/Test/TestAttrDefs.td
@@ -270,7 +270,7 @@
 // An array of nested attributes.
 def TestArrayOfUglyAttrs : ArrayOfAttr<Test_Dialect, "ArrayOfUglyAttrs",
     "array_of_ugly", "TestAttrUglyAttr"> {
-  let assemblyFormat = "`[` $value ` ` `]`";
+  let assemblyFormat = "`[` (`]`) : ($value^ ` ` `]`)?";
 }
 
 // An array of integers.