diff --git a/src/main/java/me/blvckbytes/bbconfigmapper/YamlConfig.java b/src/main/java/me/blvckbytes/bbconfigmapper/YamlConfig.java
index dc5ee09..cf5b962 100644
--- a/src/main/java/me/blvckbytes/bbconfigmapper/YamlConfig.java
+++ b/src/main/java/me/blvckbytes/bbconfigmapper/YamlConfig.java
@@ -47,6 +47,29 @@
 
 public class YamlConfig implements IConfig {
 
+  private static class LocateNodeResult {
+    private final @Nullable Node node;
+    private final boolean markedForExpressions;
+    private final Stack<MappingNode> containerStack;
+
+    private LocateNodeResult(
+      @Nullable Node node,
+      boolean markedForExpressions,
+      Stack<MappingNode> containerStack
+    ) {
+      this.node = node;
+      this.markedForExpressions = markedForExpressions;
+      this.containerStack = containerStack;
+    }
+
+    @Nullable MappingNode getLastContainer() {
+      if (containerStack.isEmpty())
+        return null;
+
+      return containerStack.pop();
+    }
+  }
+
   /*
     TODO: Add more debug logging calls to capture all details
    */
@@ -309,7 +332,7 @@ private boolean isKeyCommentedOut(String key, Node container) {
     // For lists, on the ScalarNode-s of items
     // If a comment is at the end of the file, it'll be an EndComment on the root MappingNode
 
-    Predicate<CommentLine> commentedKeyMatcher = (comment) -> comment.getValue().trim().startsWith(key + ": ");
+    Predicate<CommentLine> commentedKeyMatcher = (comment) -> comment.getValue().trim().startsWith(key + ":");
 
     // Possibly, a key which is not the last has been commented out
     if (container instanceof MappingNode) {
@@ -368,15 +391,11 @@ public int extendMissingKeys(YamlConfig other) {
         return false;
 
       String key = ((ScalarNode) tuple.getKeyNode()).getValue();
-      int lastPathDotIndex = pathOfTuple.lastIndexOf('.');
-
-      if (lastPathDotIndex > 0) {
-        String parentPath = pathOfTuple.substring(0, lastPathDotIndex);
-        Node parentNode = locateNode(parentPath, false, false).a;
+      LocateNodeResult locateResult = locateNode(pathOfTuple, true, false);
+      Node parentNode = locateResult.getLastContainer();
 
-        if (isKeyCommentedOut(key, parentNode))
-          return false;
-      }
+      if (parentNode != null && isKeyCommentedOut(key, parentNode))
+        return false;
 
       MappingNode container = locateContainerNode(pathOfTuple, true).a;
       List<NodeTuple> containerTuples = container.getValue();
@@ -433,8 +452,8 @@ private int forEachKeyPathRecursively(MappingNode node, @Nullable String parentP
   public @Nullable Object get(@Nullable String path) {
     logger.log(Level.FINEST, () -> DebugLogSource.YAML + "Object at path=" + path + " has been requested");
 
-    Tuple<@Nullable Node, Boolean> target = locateNode(path, false, false);
-    Object value = target.a == null ? null : unwrapNode(target.a, target.b);
+    LocateNodeResult target = locateNode(path, false, false);
+    Object value = target.node == null ? null : unwrapNode(target.node, target.markedForExpressions);
 
     logger.log(Level.FINEST, () -> DebugLogSource.YAML + "Returning content of path=" + path + " with value=" + value);
 
@@ -487,7 +506,7 @@ public boolean exists(@Nullable String path) {
 
     // For a key to exist, it's path has to exist within the
     // config, even if it points at a null value
-    boolean exists = locateNode(path, true, false).a != null;
+    boolean exists = locateNode(path, true, false).node != null;
 
     logger.log(Level.FINEST, () -> DebugLogSource.YAML + "Returning existence value for path=" + path + " of exists=" + exists);
 
@@ -498,7 +517,7 @@ public boolean exists(@Nullable String path) {
   public void attachComment(@Nullable String path, List<String> lines, boolean self) {
     logger.log(Level.FINEST, () -> DebugLogSource.YAML + "Attaching a comment to path=" + path + " (self=" + self + ") of lines=" + lines + " has been requested");
 
-    Node target = locateNode(path, self, false).a;
+    Node target = locateNode(path, self, false).node;
 
     if (target == null)
       throw new IllegalStateException("Cannot attach a comment to a non-existing path");
@@ -517,7 +536,7 @@ public void attachComment(@Nullable String path, List<String> lines, boolean sel
   public @Nullable List<String> readComment(@Nullable String path, boolean self) {
     logger.log(Level.FINEST, () -> DebugLogSource.YAML + "Reading the comment at path=" + path + " (self=" + self + ") has been requested");
 
-    Node target = locateNode(path, self, false).a;
+    Node target = locateNode(path, self, false).node;
 
     if (target == null)
       return null;
@@ -554,7 +573,7 @@ private Tuple<MappingNode, String> locateContainerNode(String keyPath, boolean f
     // Look up the container by the path provided before the last dot (in force mapping creation mode)
     else {
       keyPart = keyPath.substring(lastDotIndex + 1);
-      container = (MappingNode) locateNode(keyPath.substring(0, lastDotIndex), false, forceCreateMappings).a;
+      container = (MappingNode) locateNode(keyPath.substring(0, lastDotIndex), false, forceCreateMappings).node;
     }
 
     if (container == null || StringUtils.isBlank(keyPart))
@@ -690,9 +709,9 @@ private NodeTuple createNewTuple(@Nullable Node keyNode, @Nullable String key, N
    * @return A tuple of the target node or null if the target node didn't exist
    *         as well as a boolean marking whether this path was marked for expressions
    */
-  private @NotNull Tuple<@Nullable Node, Boolean> locateNode(@Nullable String path, boolean self, boolean forceCreateMappings) {
+  private @NotNull LocateNodeResult locateNode(@Nullable String path, boolean self, boolean forceCreateMappings) {
     if (path == null)
-      return new Tuple<>(rootNode, false);
+      return new LocateNodeResult(rootNode, false, null);
 
     // Keys should never contain any whitespace
     path = path.trim();
@@ -702,6 +721,7 @@ private NodeTuple createNewTuple(@Nullable Node keyNode, @Nullable String key, N
 
     Node node = rootNode;
     boolean markedForExpressions = false;
+    Stack<MappingNode> containerStack = new Stack<>();
 
     int endIndex = path.indexOf('.'), beginIndex = 0;
 
@@ -716,9 +736,12 @@ private NodeTuple createNewTuple(@Nullable Node keyNode, @Nullable String key, N
 
       // Not a mapping node, cannot look up a path-part, the key has to be invalid
       if (!(node instanceof MappingNode))
-        return new Tuple<>(null, markedForExpressions);
+        return new LocateNodeResult(null, markedForExpressions, containerStack);
 
       MappingNode mapping = (MappingNode) node;
+
+      containerStack.push(mapping);
+
       NodeTuple keyValueTuple = locateKey(mapping, pathPart);
       boolean markedAlready = expressionMarkerSuffix != null && pathPart.endsWith(expressionMarkerSuffix);
 
@@ -750,7 +773,7 @@ private NodeTuple createNewTuple(@Nullable Node keyNode, @Nullable String key, N
 
       // Current path-part does not exist
       if (keyValueTuple == null)
-        return new Tuple<>(null, markedForExpressions);
+        return new LocateNodeResult(null, markedForExpressions, containerStack);
 
       // On the last iteration and the key itself has been requested
       if (endIndex == path.length() && self)
@@ -770,7 +793,7 @@ private NodeTuple createNewTuple(@Nullable Node keyNode, @Nullable String key, N
         break;
     }
 
-    return new Tuple<>(node, markedForExpressions);
+    return new LocateNodeResult(node, markedForExpressions, containerStack);
   }
 
   /**
diff --git a/src/main/java/me/blvckbytes/bbconfigmapper/sections/AConfigSection.java b/src/main/java/me/blvckbytes/bbconfigmapper/sections/AConfigSection.java
index 0337078..f9c530a 100644
--- a/src/main/java/me/blvckbytes/bbconfigmapper/sections/AConfigSection.java
+++ b/src/main/java/me/blvckbytes/bbconfigmapper/sections/AConfigSection.java
@@ -28,13 +28,27 @@
 import org.jetbrains.annotations.Nullable;
 
 import java.lang.reflect.Field;
-import java.util.List;
+import java.util.*;
+import java.util.function.Supplier;
+import java.util.stream.Collectors;
 
 public abstract class AConfigSection {
 
+  private static class DefaultSupplier {
+    private final Supplier<Object> supplier;
+    private final Set<String> fieldExceptions;
+
+    public DefaultSupplier(Supplier<Object> supplier, Set<String> fieldExceptions) {
+      this.supplier = supplier;
+      this.fieldExceptions = fieldExceptions;
+    }
+  }
+
   private final EvaluationEnvironmentBuilder baseEnvironment;
+  private final Map<Class<?>, DefaultSupplier> fieldDefaultSuppliers;
 
   public AConfigSection(EvaluationEnvironmentBuilder baseEnvironment) {
+    this.fieldDefaultSuppliers = new HashMap<>();
     this.baseEnvironment = baseEnvironment;
   }
 
@@ -60,7 +74,7 @@ public EvaluationEnvironmentBuilder getBaseEnvironment() {
    * @param field Target field
    * @return Value to use as a default
    */
-  public @Nullable Object defaultFor(Field field) throws Exception {
+  public @Nullable Object defaultFor(Field field) {
     return null;
   }
 
@@ -68,6 +82,21 @@ public EvaluationEnvironmentBuilder getBaseEnvironment() {
    * Called when parsing of the section is completed
    * and no more changes will be applied
    */
-  public void afterParsing(List<Field> fields) throws Exception {}
+  public void afterParsing(List<Field> fields) throws Exception {
+    for (Field field : fields) {
+      if (field.get(this) != null)
+        continue;
+
+      DefaultSupplier defaultSupplier = fieldDefaultSuppliers.get(field.getType());
 
+      if (defaultSupplier == null || defaultSupplier.fieldExceptions.contains(field.getName()))
+        continue;
+
+      field.set(this, defaultSupplier.supplier.get());
+    }
+  }
+
+  protected void registerFieldDefault(Class<?> type, Supplier<Object> supplier, String... fieldExceptions) {
+    fieldDefaultSuppliers.put(type, new DefaultSupplier(supplier, Arrays.stream(fieldExceptions).collect(Collectors.toSet())));
+  }
 }
diff --git a/src/test/java/me/blvckbytes/bbconfigmapper/TestHelper.java b/src/test/java/me/blvckbytes/bbconfigmapper/TestHelper.java
index bc06ffc..174ae96 100644
--- a/src/test/java/me/blvckbytes/bbconfigmapper/TestHelper.java
+++ b/src/test/java/me/blvckbytes/bbconfigmapper/TestHelper.java
@@ -116,8 +116,9 @@ public void assertSave(String fileName, YamlConfig config) throws Exception {
     StringWriter writer = new StringWriter();
     assertDoesNotThrow(() -> config.save(writer));
     List<String> fileContents = Files.readAllLines(Paths.get("src/test/resources/save/" + fileName));
-    List<String> writerContents = Arrays.asList(writer.toString().split("\n"));
-    assertLinesMatch(fileContents, writerContents);
+    String writerString = writer.toString();
+    List<String> writerContents = Arrays.asList(writerString.split("\n"));
+    assertLinesMatch(fileContents, writerContents, "written: \n" + writerString);
   }
 
   /**
diff --git a/src/test/java/me/blvckbytes/bbconfigmapper/YamlConfigExtensionTests.java b/src/test/java/me/blvckbytes/bbconfigmapper/YamlConfigExtensionTests.java
index 6373777..510a58a 100644
--- a/src/test/java/me/blvckbytes/bbconfigmapper/YamlConfigExtensionTests.java
+++ b/src/test/java/me/blvckbytes/bbconfigmapper/YamlConfigExtensionTests.java
@@ -60,7 +60,7 @@ public void shouldExtendKeysWithScalarValues() throws Exception {
 
   @Test
   public void shouldNotExtendCommentedKeys() throws Exception {
-    char[] caseSuffixes = {'a', 'b', 'c'};
+    char[] caseSuffixes = {'a', 'b', 'c', 'd'};
 
     for (char caseSuffix : caseSuffixes) {
       YamlConfig baseConfig = helper.makeConfig("commented_keys_base_" + caseSuffix + ".yml");
diff --git a/src/test/resources/commented_keys_base_a.yml b/src/test/resources/commented_keys_base_a.yml
index 059dfc3..911eccd 100644
--- a/src/test/resources/commented_keys_base_a.yml
+++ b/src/test/resources/commented_keys_base_a.yml
@@ -5,4 +5,9 @@ a:
 #  e: 4
   f: 5
 g:
-  h: 2
\ No newline at end of file
+  h: 2
+i:
+  j:
+    k: 1
+    l: 2
+    m: 3
diff --git a/src/test/resources/commented_keys_base_b.yml b/src/test/resources/commented_keys_base_b.yml
index 059dfc3..911eccd 100644
--- a/src/test/resources/commented_keys_base_b.yml
+++ b/src/test/resources/commented_keys_base_b.yml
@@ -5,4 +5,9 @@ a:
 #  e: 4
   f: 5
 g:
-  h: 2
\ No newline at end of file
+  h: 2
+i:
+  j:
+    k: 1
+    l: 2
+    m: 3
diff --git a/src/test/resources/commented_keys_base_c.yml b/src/test/resources/commented_keys_base_c.yml
index 08b6aef..fa96925 100644
--- a/src/test/resources/commented_keys_base_c.yml
+++ b/src/test/resources/commented_keys_base_c.yml
@@ -5,4 +5,9 @@ a:
   e: 4
   f: 5
 g:
-  # h: 2
\ No newline at end of file
+  # h: 2
+i:
+  j:
+    k: 1
+    l: 2
+    m: 3
diff --git a/src/test/resources/commented_keys_base_d.yml b/src/test/resources/commented_keys_base_d.yml
new file mode 100644
index 0000000..e6c5c57
--- /dev/null
+++ b/src/test/resources/commented_keys_base_d.yml
@@ -0,0 +1,13 @@
+a:
+  b: 1
+  c: 2
+  d: 3
+  e: 4
+  f: 5
+g:
+  h: 2
+#i:
+#  j:
+#    k: 1
+#    l: 2
+#    m: 3
diff --git a/src/test/resources/commented_keys_extension.yml b/src/test/resources/commented_keys_extension.yml
index 441a0bd..33c0c7e 100644
--- a/src/test/resources/commented_keys_extension.yml
+++ b/src/test/resources/commented_keys_extension.yml
@@ -6,3 +6,8 @@ a:
   f: 5
 g:
   h: 2
+i:
+  j:
+    k: 1
+    l: 2
+    m: 3
\ No newline at end of file
diff --git a/src/test/resources/save/commented_keys_save_a.yml b/src/test/resources/save/commented_keys_save_a.yml
index 593659a..7e6b621 100644
--- a/src/test/resources/save/commented_keys_save_a.yml
+++ b/src/test/resources/save/commented_keys_save_a.yml
@@ -6,3 +6,8 @@ a:
   f: 5
 g:
   h: 2
+i:
+  j:
+    k: 1
+    l: 2
+    m: 3
diff --git a/src/test/resources/save/commented_keys_save_b.yml b/src/test/resources/save/commented_keys_save_b.yml
index 593659a..7e6b621 100644
--- a/src/test/resources/save/commented_keys_save_b.yml
+++ b/src/test/resources/save/commented_keys_save_b.yml
@@ -6,3 +6,8 @@ a:
   f: 5
 g:
   h: 2
+i:
+  j:
+    k: 1
+    l: 2
+    m: 3
diff --git a/src/test/resources/save/commented_keys_save_c.yml b/src/test/resources/save/commented_keys_save_c.yml
index 3dcff3d..6b8351b 100644
--- a/src/test/resources/save/commented_keys_save_c.yml
+++ b/src/test/resources/save/commented_keys_save_c.yml
@@ -5,4 +5,9 @@ a:
   e: 4
   f: 5
 g:
-# h: 2
\ No newline at end of file
+# h: 2
+i:
+  j:
+    k: 1
+    l: 2
+    m: 3
diff --git a/src/test/resources/save/commented_keys_save_d.yml b/src/test/resources/save/commented_keys_save_d.yml
new file mode 100644
index 0000000..e6c5c57
--- /dev/null
+++ b/src/test/resources/save/commented_keys_save_d.yml
@@ -0,0 +1,13 @@
+a:
+  b: 1
+  c: 2
+  d: 3
+  e: 4
+  f: 5
+g:
+  h: 2
+#i:
+#  j:
+#    k: 1
+#    l: 2
+#    m: 3