diff --git a/stereo/plots/plot_collection.py b/stereo/plots/plot_collection.py
index dd51df1a..2c86b46a 100644
--- a/stereo/plots/plot_collection.py
+++ b/stereo/plots/plot_collection.py
@@ -77,16 +77,15 @@ def __getattr__(self, item):
             raise AttributeError
 
         new_attr = PlotBase.get_attribute_helper(item, self.data, self.result)
+        if new_attr is None:
+            raise AttributeError(
+                f'{item} not existed, please check the function name you called!'
+            )
         if getattr(new_attr, '__download__', True):
             new_attr = download(new_attr)
-        if new_attr:
-            self.__setattr__(item, new_attr)
-            logger.info(f'register plot_func {item} to {self}')
-            return new_attr
-
-        raise AttributeError(
-            f'{item} not existed, please check the function name you called!'
-        )
+        self.__setattr__(item, new_attr)
+        logger.info(f'register plot_func {item} to {self}')
+        return new_attr
 
     @reorganize_coordinate
     def interact_cluster(
diff --git a/tests/test_plot_collection_getattr.py b/tests/test_plot_collection_getattr.py
new file mode 100644
index 00000000..08df30e1
--- /dev/null
+++ b/tests/test_plot_collection_getattr.py
@@ -0,0 +1,111 @@
+"""Test that PlotCollection.__getattr__ properly handles None from get_attribute_helper.
+
+Tests the fix for issue #454: TypeError: 'NoneType' object is not callable.
+The bug was that when get_attribute_helper returned None, the download decorator
+wrapped None, creating a callable that crashes with TypeError when invoked.
+"""
+import ast
+import pytest
+
+
+def test_getattr_none_guard_in_source():
+    """Verify that the fixed __getattr__ checks for None before applying download."""
+    with open('stereo/plots/plot_collection.py', 'r') as f:
+        source = f.read()
+
+    tree = ast.parse(source)
+
+    for node in ast.walk(tree):
+        if isinstance(node, ast.ClassDef) and node.name == 'PlotCollection':
+            for item in node.body:
+                if isinstance(item, ast.FunctionDef) and item.name == '__getattr__':
+                    source_lines = source.split('\n')
+                    func_start = item.lineno - 1
+                    func_end = item.end_lineno
+                    func_source = '\n'.join(source_lines[func_start:func_end])
+
+                    assert 'new_attr is None' in func_source or 'new_attr is not None' in func_source, \
+                        "The __getattr__ method must check for None before applying download"
+
+                    none_check_line = -1
+                    download_apply_line = -1
+                    for i, line in enumerate(func_source.split('\n')):
+                        if 'new_attr is None' in line or 'new_attr is not None' in line:
+                            none_check_line = i
+                        if 'download(new_attr)' in line:
+                            download_apply_line = i
+
+                    assert none_check_line != -1, "None check not found in __getattr__"
+                    assert download_apply_line != -1, "download(new_attr) not found in __getattr__"
+                    assert none_check_line < download_apply_line, \
+                        "None check must come BEFORE download(new_attr)"
+                    return
+
+    pytest.fail("PlotCollection.__getattr__ not found in source")
+
+
+def test_fix_logic_correctness():
+    """Directly test the fixed logic vs buggy logic to confirm the fix works."""
+    from functools import wraps
+
+    def download(func):
+        @wraps(func)
+        def wrapped(*args, **kwargs):
+            fig = func(*args, **kwargs)
+            return fig
+        return wrapped
+
+    def fixed_getattr(new_attr, item):
+        """The FIXED __getattr__ logic."""
+        if new_attr is None:
+            raise AttributeError(
+                f'{item} not existed, please check the function name you called!'
+            )
+        if getattr(new_attr, '__download__', True):
+            new_attr = download(new_attr)
+        return new_attr
+
+    def buggy_getattr(new_attr, item):
+        """The BUGGY __getattr__ logic (before fix)."""
+        if getattr(new_attr, '__download__', True):
+            new_attr = download(new_attr)
+        if new_attr:
+            return new_attr
+        raise AttributeError(
+            f'{item} not existed, please check the function name you called!'
+        )
+
+    with pytest.raises(AttributeError, match='paga_plot not existed'):
+        fixed_getattr(None, 'paga_plot')
+
+    buggy_result = buggy_getattr(None, 'paga_plot')
+    assert callable(buggy_result), "Buggy code wraps None into a callable"
+    with pytest.raises(TypeError, match="'NoneType' object is not callable"):
+        buggy_result()
+
+    def sample_plot():
+        return "figure"
+
+    result = fixed_getattr(sample_plot, 'sample_plot')
+    assert callable(result)
+    assert result() == "figure"
+
+
+def test_download_decorator_with_none():
+    """Verify the download decorator behavior when func is None."""
+    from functools import wraps
+    from matplotlib.figure import Figure
+
+    def download(func):
+        @wraps(func)
+        def wrapped(*args, **kwargs):
+            out_path = kwargs.pop('out_path', None)
+            fig = func(*args, **kwargs)
+            return fig
+        return wrapped
+
+    wrapped_none = download(None)
+    assert callable(wrapped_none), "download(None) creates a callable wrapper"
+
+    with pytest.raises(TypeError):
+        wrapped_none()