diff --git a/_extensions/cps/__init__.py b/_extensions/cps/__init__.py
index 04e6d28..08f8649 100644
--- a/_extensions/cps/__init__.py
+++ b/_extensions/cps/__init__.py
@@ -161,15 +161,22 @@ def make_list(self, values, nodetype, classes):
 
     # -------------------------------------------------------------------------
     def parse_type(self, typedesc):
-        if '|' in typedesc:
-            types = typedesc.split('|')
-            content = self.parse_type(types[0])
-            for t in types[1:]:
-                content += [
-                    nodes.Text(' '),
-                    nodes.inline('or', 'or', classes=['separator']),
-                    nodes.Text(' '),
-                ] + self.parse_type(t)
+        types = jsb.split_typedesc(typedesc)
+        if len(types) > 1:
+            if len(types) == 2 and 'null' in types:
+                types.remove('null')
+                content = [
+                    nodes.Text('(nullable) '),
+                ] + self.parse_type(types[0])
+
+            else:
+                content = self.parse_type(types[0])
+                for t in types[1:]:
+                    content += [
+                        nodes.Text(' '),
+                        nodes.inline('or', 'or', classes=['separator']),
+                        nodes.Text(' '),
+                    ] + self.parse_type(t)
 
             return content
 
diff --git a/_packages/jsb.py b/_packages/jsb.py
index 4f10b28..3bb7462 100644
--- a/_packages/jsb.py
+++ b/_packages/jsb.py
@@ -10,6 +10,28 @@ def decompose_typedesc(typedesc):
     m = re.match(r'^(list|map)[(](.*)[)]$', typedesc)
     return m.groups() if m else (None, typedesc)
 
+# =============================================================================
+def split_typedesc(typedesc):
+    assert typedesc.count('(') == typedesc.count(')')
+
+    types = []
+    start = 0
+    depth = 0
+    for n in range(len(typedesc)):
+        if typedesc[n] == '(':
+            depth += 1
+        elif typedesc[n] == ')':
+            assert depth > 0
+            depth -= 1
+        elif depth == 0 and typedesc[n] == '|':
+            types.append(typedesc[start:n])
+            start = n + 1
+
+    types.append(typedesc[start:])
+
+    print(f'split typedesc {typedesc!r} => {types!r}')
+    return types
+
 # =============================================================================
 class JsonSchema:
     # -------------------------------------------------------------------------
@@ -29,8 +51,8 @@ def add_type(self, typedesc):
             # Type already defined; nothing to do
             return
 
-        if '|' in typedesc:
-            types = typedesc.split('|')
+        types = split_typedesc(typedesc)
+        if len(types) > 1:
             for t in types:
                 self.add_type(t)
 
diff --git a/schema.rst b/schema.rst
index b7d45e2..b014b32 100644
--- a/schema.rst
+++ b/schema.rst
@@ -248,7 +248,7 @@ Attribute names are case sensitive.
 
 .. ----------------------------------------------------------------------------
 .. cps:attribute:: definitions
-  :type: map(map(string))
+  :type: map(map(string|null))
   :context: component configuration
 
   Specifies a collection of compile definitions that must be defined