PropertyProxy: fix append to empty default HandleArray

Appending to an empty default HandleArray was not possible. Fix and add
unit test.

GaudiKernel/python/GaudiKernel/PropertyProxy.py

@@ -207,8 +207,6 @@ class GaudiHandlePropertyProxyBase(PropertyProxy):
         self._handleType = handleType
         self._confTypeName = "Configurable" + handleType.componentType
 
-    #      print "%s: %r (%s)" % (self.__class__.__name__,self._handleType,self._confTypeName)
-
     def __get__(self, obj, type=None):
         try:
             return self.descr.__get__(obj, type)
@@ -217,8 +215,9 @@ class GaudiHandlePropertyProxyBase(PropertyProxy):
             try:
                 default = obj.__class__.getDefaultProperty(self.descr.__name__)
                 default = self.convertDefaultToBeSet(obj, default)
-                if default:
+                if default is not None:
                     self.__set__(obj, default)
+
             except AttributeError as e:
                 # change type of exception to avoid false error message
                 raise RuntimeError(*e.args)

GaudiKernel/tests/pytest/test_Configurables.py

@@ -11,6 +11,7 @@
 import pytest
 from GaudiKernel.Configurable import Configurable, ConfigurableAlgorithm
 from GaudiKernel.DataHandle import DataHandle
+from GaudiKernel.GaudiHandles import PublicToolHandleArray
 
 
 # Prepare dummy configurables
@@ -22,6 +23,7 @@ class MyAlg(ConfigurableAlgorithm):
         "Dict": {},
         "List": [],
         "Set": set(),
+        "ToolHandleArray": PublicToolHandleArray(),
     }
 
     def getDlls(self):
@@ -51,6 +53,7 @@ def test_correct():
     a.Dict = {"a": 1}
     a.List = [1, 2]
     a.Set = {1, 2}
+    a.ToolHandleArray = ["foo/bar"]
     assert a.getValuedProperties() == {
         "Int": 42,
         "Text": "value",
@@ -58,6 +61,7 @@ def test_correct():
         "Dict": {"a": 1},
         "List": [1, 2],
         "Set": {1, 2},
+        "ToolHandleArray": PublicToolHandleArray(["foo/bar"]),
     }
 
 
@@ -67,6 +71,12 @@ def test_str_from_datahandle():
     assert a.getProp("Text") == "value"
 
 
+def test_default_handle_append():
+    a = MyAlg()
+    a.ToolHandleArray += ["foo/bar"]
+    assert a.ToolHandleArray == PublicToolHandleArray(["foo/bar"])
+
+
 def test_invalid_value():
     a = MyAlg()