diff --git a/PersonalFinancesService/src/main/java/dev/mvvasilev/finances/entity/Categorization.java b/PersonalFinancesService/src/main/java/dev/mvvasilev/finances/entity/Categorization.java
index 0fa2e8c..8d501d3 100644
--- a/PersonalFinancesService/src/main/java/dev/mvvasilev/finances/entity/Categorization.java
+++ b/PersonalFinancesService/src/main/java/dev/mvvasilev/finances/entity/Categorization.java
@@ -22,6 +22,8 @@ public class Categorization extends AbstractEntity implements UserOwned {
     @Convert(converter = CategorizationRule.JpaConverter.class)
     private CategorizationRule categorizationRule;
 
+    private boolean isRoot;
+
     private String stringValue;
 
     private Double numericGreaterThan;
@@ -149,4 +151,12 @@ public class Categorization extends AbstractEntity implements UserOwned {
     public void setRightCategorizationId(Long rightCategorizationId) {
         this.rightCategorizationId = rightCategorizationId;
     }
+
+    public boolean isRoot() {
+        return isRoot;
+    }
+
+    public void setRoot(boolean root) {
+        isRoot = root;
+    }
 }
diff --git a/PersonalFinancesService/src/main/java/dev/mvvasilev/finances/enums/CategorizationRule.java b/PersonalFinancesService/src/main/java/dev/mvvasilev/finances/enums/CategorizationRule.java
index 9a2c15c..fea625e 100644
--- a/PersonalFinancesService/src/main/java/dev/mvvasilev/finances/enums/CategorizationRule.java
+++ b/PersonalFinancesService/src/main/java/dev/mvvasilev/finances/enums/CategorizationRule.java
@@ -8,6 +8,7 @@ public enum CategorizationRule implements PersistableEnum<String> {
     STRING_REGEX(RawTransactionValueType.STRING),
     STRING_EQ(RawTransactionValueType.STRING),
     STRING_CONTAINS(RawTransactionValueType.STRING),
+    STRING_IS_EMPTY(RawTransactionValueType.STRING),
     NUMERIC_GREATER_THAN(RawTransactionValueType.NUMERIC),
     NUMERIC_LESS_THAN(RawTransactionValueType.NUMERIC),
     NUMERIC_EQUALS(RawTransactionValueType.NUMERIC),
diff --git a/PersonalFinancesService/src/main/java/dev/mvvasilev/finances/persistence/CategorizationRepository.java b/PersonalFinancesService/src/main/java/dev/mvvasilev/finances/persistence/CategorizationRepository.java
index 0adcc0b..7750f90 100644
--- a/PersonalFinancesService/src/main/java/dev/mvvasilev/finances/persistence/CategorizationRepository.java
+++ b/PersonalFinancesService/src/main/java/dev/mvvasilev/finances/persistence/CategorizationRepository.java
@@ -13,13 +13,11 @@ import java.util.Collection;
 @Repository
 public interface CategorizationRepository extends JpaRepository<Categorization, Long> {
 
-    // We fetch only the ones with non-null category ids
-    // because ones with null category are used in AND, OR or NOT logical operations
     @Query(
             value = """
                     SELECT cat.*
                     FROM categories.categorization AS cat
-                    WHERE user_id = :userId AND category_id IS NOT NULL
+                    WHERE user_id = :userId
                     """,
             nativeQuery = true
     )
@@ -31,7 +29,7 @@ public interface CategorizationRepository extends JpaRepository<Categorization,
                         childCats AS (
                             SELECT root.*
                             FROM categories.categorization AS root
-                            WHERE root.category_id = :categoryId
+                            WHERE root.category_id = :categoryId AND root.is_root = TRUE
                     
                             UNION ALL
                     
diff --git a/PersonalFinancesService/src/main/java/dev/mvvasilev/finances/services/CategoryService.java b/PersonalFinancesService/src/main/java/dev/mvvasilev/finances/services/CategoryService.java
index 689669e..d7e0fca 100644
--- a/PersonalFinancesService/src/main/java/dev/mvvasilev/finances/services/CategoryService.java
+++ b/PersonalFinancesService/src/main/java/dev/mvvasilev/finances/services/CategoryService.java
@@ -84,6 +84,7 @@ public class CategoryService {
 
         // Run each category's rules for all transactions in parallel to eachother
         final var futures = categorizations.stream()
+                .filter(Categorization::isRoot)
                 .collect(Collectors.groupingBy(Categorization::getCategoryId, HashMap::new, Collectors.toList()))
                 .entrySet()
                 .stream()
@@ -138,13 +139,14 @@ public class CategoryService {
     private boolean matchesRule(final Collection<Categorization> allCategorizations, final Categorization categorization, final ProcessedTransaction processedTransaction) {
         return switch (categorization.getCategorizationRule()) {
             // string operations
-            case STRING_REGEX, STRING_EQ, STRING_CONTAINS -> {
+            case STRING_REGEX, STRING_EQ, STRING_CONTAINS, STRING_IS_EMPTY -> {
                 final String fieldValue = fetchTransactionStringValue(categorization, processedTransaction);
 
                 yield switch (categorization.getCategorizationRule()) {
                     case STRING_EQ -> fieldValue.equalsIgnoreCase(categorization.getStringValue());
                     case STRING_REGEX -> fieldValue.matches(categorization.getStringValue());
-                    case STRING_CONTAINS -> fieldValue.contains(categorization.getStringValue());
+                    case STRING_CONTAINS -> fieldValue.toLowerCase().contains(categorization.getStringValue().toLowerCase());
+                    case STRING_IS_EMPTY -> fieldValue == null || fieldValue.isBlank();
                     default -> throw new CommonFinancesException("Unsupported string rule: %s", categorization.getCategorizationRule());
                 };
             }
@@ -271,7 +273,7 @@ public class CategoryService {
     public Collection<CategorizationDTO> fetchCategorizationRules(Long categoryId) {
         final var categorizations = categorizationRepository.fetchForCategory(categoryId);
         return categorizationRepository.fetchForCategory(categoryId).stream()
-                .filter(c -> c.getCategoryId() != null)
+                .filter(Categorization::isRoot)
                 .map(c -> mapCategorization(categorizations, c))
                 .toList();
     }
@@ -312,16 +314,17 @@ public class CategoryService {
         categorizationRepository.deleteAllForCategory(categoryId);
 
         return dtos.stream()
-                .map(dto -> saveCategorizationRule(categoryId, userId, dto).getId())
+                .map(dto -> saveCategorizationRule(true, categoryId, userId, dto).getId())
                 .toList();
     }
 
-    private Categorization saveCategorizationRule(Long categoryId, Integer userId, CreateCategorizationDTO dto) {
+    private Categorization saveCategorizationRule(boolean isRoot, Long categoryId, Integer userId, CreateCategorizationDTO dto) {
         // TODO: Avoid recursion
 
         final var categorization = new Categorization();
 
         categorization.setCategorizationRule(dto.rule());
+        categorization.setRoot(isRoot);
         categorization.setUserId(userId);
         categorization.setRuleBasedOn(dto.ruleBasedOn());
         categorization.setCategoryId(categoryId);
@@ -331,17 +334,17 @@ public class CategoryService {
         categorization.setNumericValue(dto.numericValue().orElse(null));
         categorization.setTimestampGreaterThan(dto.timestampGreaterThan().orElse(null));
         categorization.setTimestampLessThan(dto.timestampLessThan().orElse(null));
-        categorization.setBooleanValue(dto.booleanValue().orElse(null));
+        categorization.setBooleanValue(dto.booleanValue().orElse(false));
 
         // Only root rules have category id set, to differentiate them from non-roots
         // TODO: This smells bad. Add an isRoot property instead?
         if (dto.left() != null) {
-            final var leftCat = saveCategorizationRule(null, userId, dto.left());
+            final var leftCat = saveCategorizationRule(false, categoryId, userId, dto.left());
             categorization.setLeftCategorizationId(leftCat.getId());
         }
 
         if (dto.right() != null) {
-            final var rightCat = saveCategorizationRule(null, userId, dto.right());
+            final var rightCat = saveCategorizationRule(false, categoryId, userId, dto.right());
             categorization.setRightCategorizationId(rightCat.getId());
         }
 
diff --git a/PersonalFinancesService/src/main/resources/db/migration/V1.16__AddCategorizationIsRoot.sql b/PersonalFinancesService/src/main/resources/db/migration/V1.16__AddCategorizationIsRoot.sql
new file mode 100644
index 0000000..c42a8e5
--- /dev/null
+++ b/PersonalFinancesService/src/main/resources/db/migration/V1.16__AddCategorizationIsRoot.sql
@@ -0,0 +1 @@
+ALTER TABLE categories.categorization ADD COLUMN IF NOT EXISTS is_root BOOLEAN DEFAULT(FALSE);
\ No newline at end of file
diff --git a/frontend/src/components/categories/CategorizationRule.jsx b/frontend/src/components/categories/CategorizationRule.jsx
index 7875502..2429bc9 100644
--- a/frontend/src/components/categories/CategorizationRule.jsx
+++ b/frontend/src/components/categories/CategorizationRule.jsx
@@ -80,6 +80,7 @@ export default function CategorizationRule({ ruleData, fields, ruleTypes, onDele
             case "BOOLEAN_EQ":
             case "NUMERIC_EQUALS":
             case "STRING_EQ": return "equals";
+            case "STRING_IS_EMPTY": return "is empty";
             case "TIMESTAMP_GREATER_THAN": return "is later than";
             case "NUMERIC_GREATER_THAN": return "is greater than";
             case "TIMESTAMP_LESS_THAN": return "is earlier than";
@@ -220,6 +221,7 @@ export default function CategorizationRule({ ruleData, fields, ruleTypes, onDele
                     />
                 </Grid>
             );
+            case "STRING_IS_EMPTY": return ("");
             case "BOOLEAN_EQ": return (
                 <Grid xs={1} lg={1}>
                     <Checkbox