diff --git a/src/main/java/practice/CandidateValidator.java b/src/main/java/practice/CandidateValidator.java
index 683be9f5..0313eb98 100644
--- a/src/main/java/practice/CandidateValidator.java
+++ b/src/main/java/practice/CandidateValidator.java
@@ -3,32 +3,29 @@
 import java.util.Arrays;
 import java.util.List;
 import java.util.function.Predicate;
-import java.util.stream.Collectors;
 import model.Candidate;
 
 public class CandidateValidator implements Predicate<Candidate> {
+    // National for being candidate
+    private static final String neededNational = "Ukrainian";
+    // Minimum required age for being candidate
     private static final int neededAge = 35;
+    // Minimum required years for being candidate
     private static final int neededPeriod = 10;
 
     @Override
     public boolean test(Candidate candidate) {
-        if (candidate == null) {
-            return false;
-        }
-        if (!candidate.getNationality().equals("Ukrainian")) {
-            return false;
-        }
-        if (candidate.getAge() < neededAge) {
-            return false;
-        }
-        if (!candidate.isAllowedToVote()) {
+        if (candidate == null
+                || !candidate.getNationality().equals(neededNational)
+                || candidate.getAge() < neededAge
+                || !candidate.isAllowedToVote()) {
             return false;
         }
         try {
             List<Integer> periodInUkraine = Arrays.stream(candidate.getPeriodsInUkr().split("-"))
                     .map(String::trim)
                     .map(Integer::valueOf)
-                    .collect(Collectors.toList());
+                    .toList();
             if (periodInUkraine.size() != 2
                     || periodInUkraine.get(1) - periodInUkraine.get(0) < neededPeriod) {
                 return false;
diff --git a/src/main/java/practice/StreamPractice.java b/src/main/java/practice/StreamPractice.java
index 555520d0..5551dc41 100644
--- a/src/main/java/practice/StreamPractice.java
+++ b/src/main/java/practice/StreamPractice.java
@@ -1,7 +1,6 @@
 package practice;
 
 import java.util.Arrays;
-import java.util.Collections;
 import java.util.List;
 import java.util.NoSuchElementException;
 import java.util.stream.Collectors;
@@ -19,13 +18,9 @@ public class StreamPractice {
      * "Can't get min value from list: < Here is our input 'numbers' >"
      */
     public int findMinEvenNumber(List<String> numbers) {
-        if (numbers == null || numbers.isEmpty()) {
-            throw new RuntimeException("Can't get min value from list");
-        }
+
         return numbers.stream()
-                .map(s -> s.split(","))
-                .flatMap(Arrays::stream)
-                .map(String::trim)
+                .flatMap(s -> Arrays.stream(s.split(",")))
                 .map(Integer::valueOf)
                 .filter(i -> i % 2 == 0)
                 .min(Integer::compareTo)
@@ -40,9 +35,7 @@ public int findMinEvenNumber(List<String> numbers) {
      * But before that subtract 1 from each element on an odd position (having the odd index).
      */
     public Double getOddNumsAverage(List<Integer> numbers) {
-        if (numbers == null || numbers.isEmpty()) {
-            return 0D;
-        }
+
         return IntStream.range(0, numbers.size())
                 .map(i -> i % 2 == 1 ? numbers.get(i) - 1 : numbers.get(i))
                 .filter(num -> num % 2 != 0)
@@ -59,9 +52,7 @@ public Double getOddNumsAverage(List<Integer> numbers) {
      * Example: select men who can be recruited to army (from 18 to 27 years old inclusively).
      */
     public List<Person> selectMenByAge(List<Person> peopleList, int fromAge, int toAge) {
-        if (peopleList == null || peopleList.isEmpty()) {
-            return Collections.emptyList();
-        }
+
         return peopleList.stream()
                 .filter(p -> p.getAge() >= fromAge && p.getAge() <= toAge)
                 .filter(p -> p.getSex() == Person.Sex.MAN)
@@ -80,9 +71,7 @@ public List<Person> selectMenByAge(List<Person> peopleList, int fromAge, int toA
      */
     public List<Person> getWorkablePeople(int fromAge, int femaleToAge,
                                           int maleToAge, List<Person> peopleList) {
-        if (peopleList == null || peopleList.isEmpty()) {
-            return Collections.emptyList();
-        }
+
         return peopleList.stream()
                 .filter(p -> p.getAge() >= fromAge)
                 .filter((p -> (p.getSex() == Person.Sex.WOMAN && p.getAge() <= femaleToAge)
@@ -96,9 +85,7 @@ public List<Person> getWorkablePeople(int fromAge, int femaleToAge,
      * return the names of all cats whose owners are women from `femaleAge` years old inclusively.
      */
     public List<String> getCatsNames(List<Person> peopleList, int femaleAge) {
-        if (peopleList == null || peopleList.isEmpty()) {
-            return Collections.emptyList();
-        }
+
         return peopleList.stream()
                 .filter(p -> p.getSex() == Person.Sex.WOMAN)
                 .filter(p -> p.getAge() >= femaleAge)
@@ -120,9 +107,7 @@ public List<String> getCatsNames(List<Person> peopleList, int femaleAge) {
      * parametrized with Candidate in CandidateValidator.
      */
     public List<String> validateCandidates(List<Candidate> candidates) {
-        if (candidates == null || candidates.isEmpty()) {
-            return Collections.emptyList();
-        }
+
         return candidates.stream()
                 .filter(new CandidateValidator())
                 .map(Candidate::getName)