Make sure to handle Uninferable by returning it rather than returning an exception

astroid/brain/brain_builtin_inference.py

@@ -550,6 +550,8 @@ def infer_isinstance(callnode, context=None):
         raise UseInferenceDefault("TypeError: " + str(exc))
     except AstroidError:
         raise UseInferenceDefault
+    if isinstance_bool is util.Uninferable:
+        raise UseInferenceDefault
     return nodes.Const(isinstance_bool)

astroid/helpers.py

@@ -100,8 +100,8 @@ def object_isinstance(node, class_or_seq, context=None):
         class_seq = class_or_seq
     obj_type = object_type(node, context)
     if obj_type is util.Uninferable:
-        return exceptions.InferenceError(
-            "{node} cannot be inferred".format(node=node))
+        return util.Uninferable
+
     # Instances are not types
     class_seq = [item if not isinstance(item, bases.Instance)
                  else util.Uninferable for item in class_seq]

astroid/tests/unittest_brain.py

@@ -997,6 +997,10 @@ class TestIsinstanceInference:
         with pytest.raises(astroid.InferenceError):
             _get_result_node("isinstance(1, int, str)")
+    def test_first_param_is_uninferable(self):
+        with pytest.raises(astroid.InferenceError):
+            _get_result_node('isinstance(something, int)')
+
 def _get_result_node(code):
     node = next(astroid.extract_node(code).infer())