From b849cbb60210b43c18195cc713bed8b44cc8610c Mon Sep 17 00:00:00 2001
From: Piotr Idzik <65706193+vil02@users.noreply.github.com>
Date: Sun, 22 Sep 2024 11:20:23 +0200
Subject: [PATCH] fix: handle Null Dereference in `UnitsConverter` (#5460)

---
 .inferconfig                                             | 1 -
 .../com/thealgorithms/conversions/UnitsConverter.java    | 3 ++-
 .../thealgorithms/conversions/UnitsConverterTest.java    | 9 +++++++++
 3 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/.inferconfig b/.inferconfig
index 96c34a54a..93bd1c355 100644
--- a/.inferconfig
+++ b/.inferconfig
@@ -2,7 +2,6 @@
     "report-block-list-path-regex": [
         "src/main/java/com/thealgorithms/ciphers/a5/CompositeLFSR.java",
         "src/main/java/com/thealgorithms/conversions/RomanToInteger.java",
-        "src/main/java/com/thealgorithms/conversions/UnitsConverter.java",
         "src/main/java/com/thealgorithms/datastructures/crdt/GCounter.java",
         "src/main/java/com/thealgorithms/datastructures/crdt/PNCounter.java",
         "src/main/java/com/thealgorithms/datastructures/graphs/KahnsAlgorithm.java",
diff --git a/src/main/java/com/thealgorithms/conversions/UnitsConverter.java b/src/main/java/com/thealgorithms/conversions/UnitsConverter.java
index a19d40285..81c4d4562 100644
--- a/src/main/java/com/thealgorithms/conversions/UnitsConverter.java
+++ b/src/main/java/com/thealgorithms/conversions/UnitsConverter.java
@@ -3,6 +3,7 @@ package com.thealgorithms.conversions;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Map;
+import java.util.NoSuchElementException;
 import java.util.Set;
 import org.apache.commons.lang3.tuple.Pair;
 
@@ -77,7 +78,7 @@ public final class UnitsConverter {
             throw new IllegalArgumentException("inputUnit must be different from outputUnit.");
         }
         final var conversionKey = Pair.of(inputUnit, outputUnit);
-        return conversions.get(conversionKey).convert(value);
+        return conversions.computeIfAbsent(conversionKey, k -> { throw new NoSuchElementException("No converter for: " + k); }).convert(value);
     }
 
     public Set<String> availableUnits() {
diff --git a/src/test/java/com/thealgorithms/conversions/UnitsConverterTest.java b/src/test/java/com/thealgorithms/conversions/UnitsConverterTest.java
index 76e48f144..580a66bc0 100644
--- a/src/test/java/com/thealgorithms/conversions/UnitsConverterTest.java
+++ b/src/test/java/com/thealgorithms/conversions/UnitsConverterTest.java
@@ -4,6 +4,7 @@ import static java.util.Map.entry;
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import java.util.Map;
+import java.util.NoSuchElementException;
 import org.apache.commons.lang3.tuple.Pair;
 import org.junit.jupiter.api.Test;
 
@@ -15,4 +16,12 @@ public class UnitsConverterTest {
         assertThrows(IllegalArgumentException.class, () -> someConverter.convert("A", "A", 20.0));
         assertThrows(IllegalArgumentException.class, () -> someConverter.convert("B", "B", 20.0));
     }
+
+    @Test
+    void testConvertThrowsForUnknownUnits() {
+        final UnitsConverter someConverter = new UnitsConverter(Map.ofEntries(entry(Pair.of("A", "B"), new AffineConverter(10.0, -20.0))));
+        assertThrows(NoSuchElementException.class, () -> someConverter.convert("A", "X", 20.0));
+        assertThrows(NoSuchElementException.class, () -> someConverter.convert("X", "A", 20.0));
+        assertThrows(NoSuchElementException.class, () -> someConverter.convert("X", "Y", 20.0));
+    }
 }