Add command NULLIF for identifying nulls in LOAD CSV (#914)

Add NULLIF command which turns all row values corresponding to the string to the nullif character sequence.

tests/e2e/load_csv/CMakeLists.txt

@@ -8,3 +8,6 @@ endfunction()
 
 copy_load_csv_e2e_python_files(load_csv.py)
 copy_load_csv_e2e_files(simple.csv)
+
+copy_load_csv_e2e_python_files(load_csv_nullif.py)
+copy_load_csv_e2e_files(nullif.csv)

tests/e2e/load_csv/load_csv_nullif.py

@@ -0,0 +1,53 @@
+# Copyright 2022 Memgraph Ltd.
+#
+# Use of this software is governed by the Business Source License
+# included in the file licenses/BSL.txt; by using this file, you agree to be bound by the terms of the Business Source
+# License, and you may not use this file except in compliance with the Business Source License.
+#
+# As of the Change Date specified in that file, in accordance with
+# the Business Source License, use of this software will be governed
+# by the Apache License, Version 2.0, included in the file
+# licenses/APL.txt.
+
+import os
+import sys
+from pathlib import Path
+
+import pytest
+from gqlalchemy import Memgraph
+
+NULLIF_CSV_FILE = "nullif.csv"
+
+
+def get_file_path(file: str) -> str:
+    parent_path = Path(__file__).parent.absolute()
+    return os.path.join(parent_path, file)
+
+
+def test_given_csv_when_nullif_then_all_identical_rows_are_null():
+    memgraph = Memgraph("localhost", 7687)
+
+    results = list(
+        memgraph.execute_and_fetch(
+            f"""LOAD CSV FROM '{get_file_path(NULLIF_CSV_FILE)}'
+            WITH HEADER NULLIF 'N/A' AS row
+            CREATE (n:Person {{name: row.name, age: row.age,
+            percentage: row.percentage, works_in_IT: row.works_in_IT}})
+            RETURN n
+            """
+        )
+    )
+
+    expected_properties = [
+        {"age": "10", "percentage": "15.0", "works_in_IT": "false"},
+        {"name": "John", "percentage": "35.4", "works_in_IT": "false"},
+        {"name": "Milewa", "age": "34", "works_in_IT": "false"},
+        {"name": "Lucas", "age": "50", "percentage": "12.5"},
+    ]
+    properties = [result["n"]._properties for result in results]
+
+    assert expected_properties == properties
+
+
+if __name__ == "__main__":
+    sys.exit(pytest.main([__file__, "-rA"]))

tests/e2e/load_csv/nullif.csv

@@ -0,0 +1,5 @@
+name,age,percentage,works_in_IT
+N/A,10,15.0,false
+John,N/A,35.4,false
+Milewa,34,N/A,false
+Lucas,50,12.5,N/A

tests/e2e/load_csv/workloads.yaml

@@ -1,3 +1,10 @@
+nullif_cluster: &nullif_cluster
+  cluster:
+    main:
+      args: ["--bolt-port", "7687", "--log-level=TRACE"]
+      log_file: "load_csv_log_file.txt"
+      validation_queries: []
+
 load_csv_cluster: &load_csv_cluster
   cluster:
     main:
@@ -9,6 +16,10 @@ load_csv_cluster: &load_csv_cluster
       validation_queries: []
 
 workloads:
+  - name: "LOAD CSV nullif"
+    binary: "tests/e2e/pytest_runner.sh"
+    args: ["load_csv/load_csv_nullif.py"]
+    <<: *nullif_cluster
   - name: "MATCH + LOAD CSV"
     binary: "tests/e2e/pytest_runner.sh"
     args: ["load_csv/load_csv.py"]