diff --git a/lib/src/ensure.dart b/lib/src/ensure.dart
index 83b7fa0..b589a38 100644
--- a/lib/src/ensure.dart
+++ b/lib/src/ensure.dart
@@ -6,27 +6,27 @@ bool ensureCase(dynamic raw, Case target) {
   if (raw is Iterable) {
     return raw.isEmpty || raw.every((element) => ensureCase(element, target));
   }
-  if (raw is! String) {
-    return false;
-  }
-  switch (target) {
-    case Case.lower:
-      return raw.toLowerCase() == raw;
-    case Case.upper:
-      return raw.toUpperCase() == raw;
-    case Case.camel:
-      return raw.toCamelCase() == raw;
-    case Case.kebab:
-      return raw.toKebabCase() == raw;
-    case Case.pascal:
-      return raw.toPascalCase() == raw;
-    case Case.sentence:
-      return raw.toSentenceCase() == raw;
-    case Case.snake:
-      return raw.toSnakeCase() == raw;
-    case Case.capital:
-      return raw.toCapitalCase() == raw;
+  if (raw is String) {
+    switch (target) {
+      case Case.lower:
+        return raw.toLowerCase() == raw;
+      case Case.upper:
+        return raw.toUpperCase() == raw;
+      case Case.camel:
+        return raw.toCamelCase() == raw;
+      case Case.kebab:
+        return raw.toKebabCase() == raw;
+      case Case.pascal:
+        return raw.toPascalCase() == raw;
+      case Case.sentence:
+        return raw.toSentenceCase() == raw;
+      case Case.snake:
+        return raw.toSnakeCase() == raw;
+      case Case.capital:
+        return raw.toCapitalCase() == raw;
+    }
   }
+  return false;
 }
 
 bool ensureFullStop(String raw, String target) {
@@ -38,9 +38,6 @@ bool ensureLeadingBlank(String raw) {
 }
 
 bool ensureMaxLength(dynamic raw, num maxLength) {
-  if (raw == null) {
-    return true;
-  }
   if (raw is String) {
     return raw.length <= maxLength;
   }
@@ -51,13 +48,12 @@ bool ensureMaxLength(dynamic raw, num maxLength) {
 }
 
 bool ensureMaxLineLength(String raw, num maxLineLength) {
-  return raw.split('\n').every((line) => ensureMaxLength(line, maxLineLength));
+  return raw
+      .split(RegExp(r'(?:\r?\n)'))
+      .every((line) => ensureMaxLength(line, maxLineLength));
 }
 
 bool ensureMinLength(dynamic raw, num minLength) {
-  if (raw == null) {
-    return false;
-  }
   if (raw is String) {
     return raw.length >= minLength;
   }
@@ -68,9 +64,6 @@ bool ensureMinLength(dynamic raw, num minLength) {
 }
 
 bool ensureEmpty(dynamic raw) {
-  if (raw == null) {
-    return true;
-  }
   if (raw is String) {
     return raw.isEmpty;
   }
@@ -81,9 +74,6 @@ bool ensureEmpty(dynamic raw) {
 }
 
 bool ensureEnum(dynamic raw, Iterable enums) {
-  if (raw == null) {
-    return true;
-  }
   if (raw is String) {
     return raw.isEmpty || enums.contains(raw);
   }
diff --git a/lib/src/rules.dart b/lib/src/rules.dart
index 116b884..bc5f684 100644
--- a/lib/src/rules.dart
+++ b/lib/src/rules.dart
@@ -39,14 +39,14 @@ Map<String, RuleFunction> get supportedRules => {
       'references-empty': emptyRule(CommitComponent.references),
     };
 
-/// Build full stop rule for commit component.
+/// Build full-stop rule for commit component.
 RuleFunction fullStopRule(CommitComponent component) {
   return (Commit commit, Rule config) {
     if (config is! ValueRule) {
       throw Exception('$config is not ValueRuleConfig<String>');
     }
     final raw = commit.componentRaw(component);
-    final result = raw != null && ensureFullStop(raw, config.value);
+    final result = raw == null || ensureFullStop(raw, config.value);
     final negated = config.condition == RuleCondition.never;
     return RuleOutcome(
       valid: negated ? !result : result,
@@ -59,11 +59,11 @@ RuleFunction fullStopRule(CommitComponent component) {
   };
 }
 
-/// Build leanding blank rule for commit component.
+/// Build leanding-blank rule for commit component.
 RuleFunction leadingBlankRule(CommitComponent component) {
   return (Commit commit, Rule config) {
     final raw = commit.componentRaw(component);
-    final result = raw != null && ensureLeadingBlank(raw);
+    final result = raw == null || ensureLeadingBlank(raw);
     final negated = config.condition == RuleCondition.never;
     return RuleOutcome(
       valid: negated ? !result : result,
@@ -76,11 +76,11 @@ RuleFunction leadingBlankRule(CommitComponent component) {
   };
 }
 
-/// Build leanding blank rule for commit component.
+/// Build empty rule for commit component.
 RuleFunction emptyRule(CommitComponent component) {
   return (Commit commit, Rule config) {
     final raw = commit.componentRaw(component);
-    final result = ensureEmpty(raw);
+    final result = raw == null || ensureEmpty(raw);
     final negated = config.condition == RuleCondition.never;
     return RuleOutcome(
       valid: negated ? !result : result,
@@ -97,7 +97,7 @@ RuleFunction caseRule(CommitComponent component) {
       throw Exception('$config is not CaseRuleConfig');
     }
     final raw = commit.componentRaw(component);
-    final result = raw != null && ensureCase(raw, config.type);
+    final result = raw == null || ensureCase(raw, config.type);
     final negated = config.condition == RuleCondition.never;
     return RuleOutcome(
       valid: negated ? !result : result,
@@ -110,14 +110,14 @@ RuleFunction caseRule(CommitComponent component) {
   };
 }
 
-/// Build max length rule for commit component.
+/// Build max-length rule for commit component.
 RuleFunction maxLengthRule(CommitComponent component) {
   return (Commit commit, Rule config) {
     if (config is! LengthRule) {
       throw Exception('$config is not LengthRuleConfig');
     }
     final raw = commit.componentRaw(component);
-    final result = raw != null && ensureMaxLength(raw, config.length);
+    final result = raw == null || ensureMaxLength(raw, config.length);
     final negated = config.condition == RuleCondition.never;
     return RuleOutcome(
       valid: negated ? !result : result,
@@ -130,14 +130,14 @@ RuleFunction maxLengthRule(CommitComponent component) {
   };
 }
 
-/// Build max line length rule for commit component.
+/// Build max-line-length rule for commit component.
 RuleFunction maxLineLengthRule(CommitComponent component) {
   return (Commit commit, Rule config) {
     if (config is! LengthRule) {
       throw Exception('$config is not LengthRuleConfig');
     }
     final raw = commit.componentRaw(component);
-    final result = raw != null && ensureMaxLineLength(raw, config.length);
+    final result = raw == null || ensureMaxLineLength(raw, config.length);
     final negated = config.condition == RuleCondition.never;
     return RuleOutcome(
       valid: negated ? !result : result,
@@ -150,14 +150,14 @@ RuleFunction maxLineLengthRule(CommitComponent component) {
   };
 }
 
-/// Build min length rule for commit component.
+/// Build min-length rule for commit component.
 RuleFunction minLengthRule(CommitComponent component) {
   return (Commit commit, Rule config) {
     if (config is! LengthRule) {
       throw Exception('$config is not LengthRuleConfig');
     }
     final raw = commit.componentRaw(component);
-    final result = raw != null && ensureMinLength(raw, config.length);
+    final result = raw == null || ensureMinLength(raw, config.length);
     final negated = config.condition == RuleCondition.never;
     return RuleOutcome(
       valid: negated ? !result : result,
@@ -170,13 +170,14 @@ RuleFunction minLengthRule(CommitComponent component) {
   };
 }
 
+/// Build enum rule for commit component.
 RuleFunction enumRule(CommitComponent component) {
   return (Commit commit, Rule config) {
     if (config is! EnumRule) {
       throw Exception('$config is not EnumRuleConfig');
     }
     final raw = commit.componentRaw(component);
-    final result = ensureEnum(raw, config.allowed);
+    final result = raw == null || ensureEnum(raw, config.allowed);
     final negated = config.condition == RuleCondition.never;
     return RuleOutcome(
       valid: negated ? !result : result,