ENH: Values can hold empty vector

Summary

Values should be able to hold empty vector. Before this MR, creating a value with an empty vector does not make this a vector.

See #76 (closed).

Focus

Nothing special.

Test Environment

Run the unit test.

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Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
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• Appropriate user and developer documentation (or not necessary)
• The test environment setup works and the intended behavior is reproducible in the test environment
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test/test_value.cpp

@@ -136,6 +136,14 @@ TEST(test_value, test_list) {
     EXPECT_EQ(item.IsString(), true);
     EXPECT_EQ(item.GetAsString(), "id" + std::to_string(counter++));
   }
+
+  // Test empty lists
+  auto empty_content = std::vector<int>();
+  Value value_0(empty_content);
+  EXPECT_TRUE(value_0.IsVector());
+  auto list_value_0 = value_0.GetAsVector();
+  EXPECT_EQ(list_value_0.size(), 0);
+  EXPECT_TRUE(list_value_0.empty());
 }
 
 TEST(test_value, test_scalar_value_to_value) {