[MO]Fix Merge shape infer function (#7864)

* Update merge shape infer function

* Update merge shape inference tests

model-optimizer/extensions/ops/merge.py

@@ -34,13 +34,15 @@ class Merge(Op):
 
             inferred_and_executable = [n for n in node.in_nodes().values() if n['is_partial_inferred'] and
                                        'executable' in n and n['executable']]
-            tensor = inferred_and_executable[0]
+            if len(inferred_and_executable) > 0:
+                tensor = inferred_and_executable[0]
 
-            if all([tensor.has_valid('value') and n.has_valid('value') and strict_compare_tensors(tensor.value, n.value)
-                    for n in inferred_and_executable]):
-                node.out_node().value = tensor.value.copy()
-            else:
-                node.out_node().value = None
+                if all([tensor.has_valid('value') and n.has_valid('value') and strict_compare_tensors(tensor.value,
+                                                                                                      n.value)
+                        for n in inferred_and_executable]):
+                    node.out_node().value = tensor.value.copy()
+                else:
+                    node.out_node().value = None
 
         # do not use set_shape(tensor.shape) here because input port shape may be different from the calculated output
         # shape and `set_shape` will raise an error that shape has changed

model-optimizer/unit_tests/extensions/ops/merge_test.py

@@ -58,7 +58,7 @@ class TestMerge(unittest.TestCase):
                                            edges_with_attrs=self.edges,
                                            update_nodes_attributes=[('second', {'executable': True}),
                                                                     ('first', {'is_partial_inferred': False,
-                                                                                'value': None}),
+                                                                               'value': None}),
                                                                     ('merge_output', {'shape': np.array([2, 2]),
                                                                                       'value': None}),
                                                                     ('merge', {'is_not_fully_inferred': True})])
@@ -115,3 +115,31 @@ class TestMerge(unittest.TestCase):
 
         (flag, resp) = compare_graphs(graph, ref_graph, 'merge_output', check_op_attrs=True)
         self.assertTrue(flag, resp)
+
+    def test_merge_infer_no_executable(self):
+        graph = build_graph_with_attrs(
+            nodes_with_attrs=self.nodes,
+            edges_with_attrs=self.edges,
+            update_nodes_attributes=[
+                ('first', {'executable': False, 'value': np.ones([2, 2]), 'shape': int64_array([2, 2])}),
+                ('second', {'executable': False, 'value': np.zeros([4, 4]), 'shape': int64_array([4, 4])})
+            ]
+        )
+
+        ref_graph = build_graph_with_attrs(
+            nodes_with_attrs=self.nodes,
+            edges_with_attrs=self.edges,
+            update_nodes_attributes=[
+                ('first', {'executable': False, 'value': np.ones([2, 2]), 'shape': int64_array([2, 2])}),
+                ('second', {'executable': False, 'value': np.zeros([4, 4]), 'shape': int64_array([4, 4])}),
+                ('merge', {'is_not_fully_inferred': False}),
+                ('merge_output', {'shape': int64_array([2, 2]), 'value': None})
+            ]
+        )
+
+        tested_class = Merge(graph=graph, attrs={})
+        node = Node(graph, 'merge')
+        tested_class.merge_infer(node)
+
+        (flag, resp) = compare_graphs(graph, ref_graph, 'merge_output', check_op_attrs=True)
+        self.assertTrue(flag, resp)