diff --git a/abstract-document/src/main/java/com/iluwatar/abstractdocument/AbstractDocument.java b/abstract-document/src/main/java/com/iluwatar/abstractdocument/AbstractDocument.java
index 665729008..701906041 100644
--- a/abstract-document/src/main/java/com/iluwatar/abstractdocument/AbstractDocument.java
+++ b/abstract-document/src/main/java/com/iluwatar/abstractdocument/AbstractDocument.java
@@ -36,41 +36,67 @@ import java.util.stream.Stream;
  */
 public abstract class AbstractDocument implements Document {
 
-  private final Map<String, Object> properties;
+  private final Map<String, Object> documentProperties;
 
   protected AbstractDocument(Map<String, Object> properties) {
     Objects.requireNonNull(properties, "properties map is required");
-    this.properties = properties;
+    this.documentProperties = properties;
   }
 
   @Override
   public Void put(String key, Object value) {
-    properties.put(key, value);
+    documentProperties.put(key, value);
     return null;
   }
 
   @Override
   public Object get(String key) {
-    return properties.get(key);
+    return documentProperties.get(key);
   }
 
   @Override
-  public <T> Stream<T> children(String key, Function<Map<String, Object>, T> constructor) {
+  public <T> Stream<T> children(String key, Function<Map<String, Object>, T> childConstructor) {
     return Stream.ofNullable(get(key))
-        .filter(Objects::nonNull)
-        .map(el -> (List<Map<String, Object>>) el)
-        .findAny()
-        .stream()
-        .flatMap(Collection::stream)
-        .map(constructor);
+            .filter(Objects::nonNull)
+            .map(el -> (List<Map<String, Object>>) el)
+            .findAny()
+            .stream()
+            .flatMap(Collection::stream)
+            .map(childConstructor);
   }
 
   @Override
   public String toString() {
+    return buildStringRepresentation();
+  }
+
+  private String buildStringRepresentation() {
     var builder = new StringBuilder();
     builder.append(getClass().getName()).append("[");
-    properties.forEach((key, value) -> builder.append("[").append(key).append(" : ").append(value)
-        .append("]"));
+
+    // Explaining variable for document properties map
+    Map<String, Object> documentProperties = this.documentProperties;
+
+    // Explaining variable for the size of document properties map
+    int numProperties = documentProperties.size();
+
+    // Explaining variable for tracking the current property index
+    int currentPropertyIndex = 0;
+
+    // Iterate over document properties map
+    for (Map.Entry<String, Object> entry : documentProperties.entrySet()) {
+      String key = entry.getKey();
+      Object value = entry.getValue();
+
+      // Append key-value pair
+      builder.append("[").append(key).append(" : ").append(value).append("]");
+
+      // Add comma if not last property
+      if (++currentPropertyIndex < numProperties) {
+        builder.append(", ");
+      }
+    }
+
     builder.append("]");
     return builder.toString();
   }
diff --git a/abstract-document/src/test/java/com/iluwatar/abstractdocument/AbstractDocumentTest.java b/abstract-document/src/test/java/com/iluwatar/abstractdocument/AbstractDocumentTest.java
index 249f01f64..a86e6273d 100644
--- a/abstract-document/src/test/java/com/iluwatar/abstractdocument/AbstractDocumentTest.java
+++ b/abstract-document/src/test/java/com/iluwatar/abstractdocument/AbstractDocumentTest.java
@@ -80,4 +80,46 @@ class AbstractDocumentTest {
     assertTrue(document.toString().contains(VALUE));
   }
 
+  @Test
+  void shouldHandleExceptionDuringConstruction() {
+    Map<String, Object> invalidProperties = null; // Invalid properties, causing NullPointerException
+
+    // Throw null pointer exception
+    assertThrows(NullPointerException.class, () -> {
+      // Attempt to construct a document with invalid properties
+      new DocumentImplementation(invalidProperties);
+    });
+  }
+
+  @Test
+  void shouldPutAndGetNestedDocument() {
+    // Creating a nested document
+    DocumentImplementation nestedDocument = new DocumentImplementation(new HashMap<>());
+    nestedDocument.put("nestedKey", "nestedValue");
+
+
+    document.put("nested", nestedDocument);
+
+    // Retrieving the nested document
+    DocumentImplementation retrievedNestedDocument = (DocumentImplementation) document.get("nested");
+
+    assertNotNull(retrievedNestedDocument);
+    assertEquals("nestedValue", retrievedNestedDocument.get("nestedKey"));
+  }
+
+  @Test
+  void shouldUpdateExistingValue() {
+    // Arrange
+    final String key = "key";
+    final String originalValue = "originalValue";
+    final String updatedValue = "updatedValue";
+
+    document.put(key, originalValue);
+
+    // Updating the value
+    document.put(key, updatedValue);
+
+    //Verifying that the updated value is retrieved correctly
+    assertEquals(updatedValue, document.get(key));
+  }
 }