diff --git a/PhpCollective/Sniffs/AbstractSniffs/AbstractSniff.php b/PhpCollective/Sniffs/AbstractSniffs/AbstractSniff.php
index d86f780..9e250cd 100644
--- a/PhpCollective/Sniffs/AbstractSniffs/AbstractSniff.php
+++ b/PhpCollective/Sniffs/AbstractSniffs/AbstractSniff.php
@@ -135,8 +135,9 @@ protected function getClassName(File $phpcsFile): string
         $fileName = $phpcsFile->getFilename();
         $fileNameParts = explode(DIRECTORY_SEPARATOR, $fileName);
         $directoryPosition = array_search('src', $fileNameParts, true);
-        if (!$directoryPosition) {
-            $directoryPosition = array_search('tests', $fileNameParts, true) + 1;
+        if ($directoryPosition === false) {
+            $testsPosition = array_search('tests', $fileNameParts, true);
+            $directoryPosition = $testsPosition === false ? 0 : $testsPosition + 1;
         }
         $classNameParts = array_slice($fileNameParts, $directoryPosition + 1);
         $className = implode('\\', $classNameParts);
diff --git a/PhpCollective/Sniffs/Classes/EnumCaseCasingSniff.php b/PhpCollective/Sniffs/Classes/EnumCaseCasingSniff.php
index b60147f..ce840ff 100644
--- a/PhpCollective/Sniffs/Classes/EnumCaseCasingSniff.php
+++ b/PhpCollective/Sniffs/Classes/EnumCaseCasingSniff.php
@@ -55,7 +55,7 @@ public function process(File $phpcsFile, $stackPtr): void
         }
 
         $result = mb_strtolower($content);
-        $result = ucfirst($result);
+        $result = mb_strtoupper(mb_substr($result, 0, 1)) . mb_substr($result, 1);
 
         if ($result === $content) {
             return;
diff --git a/PhpCollective/Sniffs/ControlStructures/NoInlineAssignmentSniff.php b/PhpCollective/Sniffs/ControlStructures/NoInlineAssignmentSniff.php
index 5088512..e8652d3 100644
--- a/PhpCollective/Sniffs/ControlStructures/NoInlineAssignmentSniff.php
+++ b/PhpCollective/Sniffs/ControlStructures/NoInlineAssignmentSniff.php
@@ -37,8 +37,8 @@ public function process(File $phpcsFile, $stackPtr): void
             return;
         }
 
-        $openingBraceIndex = (int)$phpcsFile->findNext(Tokens::$emptyTokens, ($stackPtr + 1), null, true);
-        if (!$openingBraceIndex) {
+        $openingBraceIndex = $phpcsFile->findNext(Tokens::$emptyTokens, $stackPtr + 1, null, true);
+        if ($openingBraceIndex === false) {
             return;
         }
         if (empty($tokens[$openingBraceIndex]['parenthesis_closer'])) {
@@ -113,8 +113,8 @@ protected function checkMethodCalls(File $phpcsFile, int $stackPtr): void
     {
         $tokens = $phpcsFile->getTokens();
 
-        $openingBraceIndex = $phpcsFile->findNext(T_OPEN_PARENTHESIS, ($stackPtr + 1), $stackPtr + 4);
-        if (!$openingBraceIndex) {
+        $openingBraceIndex = $phpcsFile->findNext(T_OPEN_PARENTHESIS, $stackPtr + 1, $stackPtr + 4);
+        if ($openingBraceIndex === false) {
             return;
         }
         if (empty($tokens[$openingBraceIndex]['parenthesis_closer'])) {
diff --git a/PhpCollective/Sniffs/PHP/NoIsNullSniff.php b/PhpCollective/Sniffs/PHP/NoIsNullSniff.php
index c7e9aa0..44545a2 100644
--- a/PhpCollective/Sniffs/PHP/NoIsNullSniff.php
+++ b/PhpCollective/Sniffs/PHP/NoIsNullSniff.php
@@ -100,11 +100,11 @@ public function process(File $phpcsFile, $stackPtr): void
             }
 
             if ($trailingComparison) {
-                $possibleEndIndex = $this->findUnnecessaryLeadingComparisonStart($phpcsFile, $endIndex);
-                if ($possibleEndIndex !== null) {
-                    $endIndex = $possibleEndIndex;
+                $trailingResult = $this->findUnnecessaryTrailingComparisonEnd($phpcsFile, $endIndex);
+                if ($trailingResult !== null) {
+                    $endIndex = $trailingResult['index'];
                     $trailingComparison = false;
-                    if ($tokens[$endIndex]['code'] === T_FALSE) {
+                    if ($trailingResult['negated']) {
                         $negated = !$negated;
                     }
                 }
@@ -189,13 +189,13 @@ protected function findUnnecessaryLeadingComparisonStart(File $phpcsFile, int $i
     {
         $tokens = $phpcsFile->getTokens();
 
-        $previous = (int)$phpcsFile->findPrevious(T_WHITESPACE, ($index - 1), null, true);
-        if (!$previous || !in_array($tokens[$previous]['code'], [T_IS_IDENTICAL, T_IS_NOT_IDENTICAL])) {
+        $previous = $phpcsFile->findPrevious(T_WHITESPACE, $index - 1, null, true);
+        if ($previous === false || !in_array($tokens[$previous]['code'], [T_IS_IDENTICAL, T_IS_NOT_IDENTICAL], true)) {
             return null;
         }
 
-        $previous = (int)$phpcsFile->findPrevious(T_WHITESPACE, ($previous - 1), null, true);
-        if (!$previous || !in_array($tokens[$previous]['code'], [T_TRUE, T_FALSE])) {
+        $previous = $phpcsFile->findPrevious(T_WHITESPACE, $previous - 1, null, true);
+        if ($previous === false || !in_array($tokens[$previous]['code'], [T_TRUE, T_FALSE], true)) {
             return null;
         }
 
@@ -206,23 +206,34 @@ protected function findUnnecessaryLeadingComparisonStart(File $phpcsFile, int $i
      * @param \PHP_CodeSniffer\Files\File $phpcsFile
      * @param int $index
      *
-     * @return int|null
+     * @return array{index: int, negated: bool}|null
      */
-    protected function findUnnecessaryTrailingComparisonEnd(File $phpcsFile, int $index): ?int
+    protected function findUnnecessaryTrailingComparisonEnd(File $phpcsFile, int $index): ?array
     {
         $tokens = $phpcsFile->getTokens();
 
-        $next = (int)$phpcsFile->findNext(T_WHITESPACE, ($index + 1), null, true);
-        if (!$next || !in_array($tokens[$next]['code'], [T_IS_IDENTICAL, T_IS_NOT_IDENTICAL])) {
+        $operatorIndex = $phpcsFile->findNext(T_WHITESPACE, $index + 1, null, true);
+        if ($operatorIndex === false || !in_array($tokens[$operatorIndex]['code'], [T_IS_IDENTICAL, T_IS_NOT_IDENTICAL], true)) {
             return null;
         }
 
-        $next = (int)$phpcsFile->findPrevious(T_WHITESPACE, ($next - 1), null, true);
-        if (!$next || !in_array($tokens[$next]['code'], [T_TRUE, T_FALSE])) {
+        $isNotIdentical = $tokens[$operatorIndex]['code'] === T_IS_NOT_IDENTICAL;
+
+        $valueIndex = $phpcsFile->findNext(T_WHITESPACE, $operatorIndex + 1, null, true);
+        if ($valueIndex === false || !in_array($tokens[$valueIndex]['code'], [T_TRUE, T_FALSE], true)) {
             return null;
         }
 
-        return $next;
+        $isFalse = $tokens[$valueIndex]['code'] === T_FALSE;
+
+        // Determine if negation is needed:
+        // === true -> no negation
+        // === false -> negate
+        // !== true -> negate
+        // !== false -> no negation (double negation)
+        $negated = $isNotIdentical !== $isFalse;
+
+        return ['index' => $valueIndex, 'negated' => $negated];
     }
 
     /**
diff --git a/PhpCollective/Sniffs/PHP/PhpSapiConstantSniff.php b/PhpCollective/Sniffs/PHP/PhpSapiConstantSniff.php
index 5144cf9..09782fe 100644
--- a/PhpCollective/Sniffs/PHP/PhpSapiConstantSniff.php
+++ b/PhpCollective/Sniffs/PHP/PhpSapiConstantSniff.php
@@ -42,18 +42,18 @@ public function process(File $phpcsFile, $stackPtr): void
             return;
         }
 
-        $previous = (int)$phpcsFile->findPrevious(T_WHITESPACE, ($stackPtr - 1), null, true);
-        if (!$previous || in_array($tokens[$previous]['code'], $wrongTokens)) {
+        $previous = $phpcsFile->findPrevious(T_WHITESPACE, $stackPtr - 1, null, true);
+        if ($previous === false || in_array($tokens[$previous]['code'], $wrongTokens, true)) {
             return;
         }
 
-        $openingBrace = (int)$phpcsFile->findNext(T_WHITESPACE, ($stackPtr + 1), null, true);
-        if (!$openingBrace || $tokens[$openingBrace]['type'] !== 'T_OPEN_PARENTHESIS') {
+        $openingBrace = $phpcsFile->findNext(T_WHITESPACE, $stackPtr + 1, null, true);
+        if ($openingBrace === false || $tokens[$openingBrace]['type'] !== 'T_OPEN_PARENTHESIS') {
             return;
         }
 
-        $closingBrace = (int)$phpcsFile->findNext(T_WHITESPACE, ($openingBrace + 1), null, true);
-        if (!$closingBrace || $tokens[$closingBrace]['type'] !== 'T_CLOSE_PARENTHESIS') {
+        $closingBrace = $phpcsFile->findNext(T_WHITESPACE, $openingBrace + 1, null, true);
+        if ($closingBrace === false || $tokens[$closingBrace]['type'] !== 'T_CLOSE_PARENTHESIS') {
             return;
         }
 
diff --git a/PhpCollective/Sniffs/PHP/PreferCastOverFunctionSniff.php b/PhpCollective/Sniffs/PHP/PreferCastOverFunctionSniff.php
index 2ae7799..de974c8 100644
--- a/PhpCollective/Sniffs/PHP/PreferCastOverFunctionSniff.php
+++ b/PhpCollective/Sniffs/PHP/PreferCastOverFunctionSniff.php
@@ -48,13 +48,13 @@ public function process(File $phpcsFile, $stackPtr): void
             return;
         }
 
-        $previous = (int)$phpcsFile->findPrevious(T_WHITESPACE, ($stackPtr - 1), null, true);
-        if (!$previous || in_array($tokens[$previous]['code'], $wrongTokens)) {
+        $previous = $phpcsFile->findPrevious(T_WHITESPACE, $stackPtr - 1, null, true);
+        if ($previous === false || in_array($tokens[$previous]['code'], $wrongTokens, true)) {
             return;
         }
 
-        $openingBraceIndex = (int)$phpcsFile->findNext(T_WHITESPACE, ($stackPtr + 1), null, true);
-        if (!$openingBraceIndex || $tokens[$openingBraceIndex]['type'] !== 'T_OPEN_PARENTHESIS') {
+        $openingBraceIndex = $phpcsFile->findNext(T_WHITESPACE, $stackPtr + 1, null, true);
+        if ($openingBraceIndex === false || $tokens[$openingBraceIndex]['type'] !== 'T_OPEN_PARENTHESIS') {
             return;
         }
 
diff --git a/tests/PhpCollective/Sniffs/PHP/NoIsNullSniffTest.php b/tests/PhpCollective/Sniffs/PHP/NoIsNullSniffTest.php
new file mode 100644
index 0000000..7153fbd
--- /dev/null
+++ b/tests/PhpCollective/Sniffs/PHP/NoIsNullSniffTest.php
@@ -0,0 +1,30 @@
+<?php
+
+/**
+ * MIT License
+ * For full license information, please view the LICENSE file that was distributed with this source code.
+ */
+
+namespace PhpCollective\Test\PhpCollective\Sniffs\PHP;
+
+use PhpCollective\Sniffs\PHP\NoIsNullSniff;
+use PhpCollective\Test\TestCase;
+
+class NoIsNullSniffTest extends TestCase
+{
+    /**
+     * @return void
+     */
+    public function testNoIsNullSniffer(): void
+    {
+        $this->assertSnifferFindsFixableErrors(new NoIsNullSniff(), 8, 8);
+    }
+
+    /**
+     * @return void
+     */
+    public function testNoIsNullFixer(): void
+    {
+        $this->assertSnifferCanFixErrors(new NoIsNullSniff(), 8);
+    }
+}
diff --git a/tests/_data/NoIsNull/after.php b/tests/_data/NoIsNull/after.php
new file mode 100644
index 0000000..2f08720
--- /dev/null
+++ b/tests/_data/NoIsNull/after.php
@@ -0,0 +1,70 @@
+<?php declare(strict_types = 1);
+
+namespace PhpCollective;
+
+class FixMe
+{
+    /**
+     * Basic is_null() should become === null
+     */
+    public function basicIsNull($x): bool
+    {
+        return $x === null;
+    }
+
+    /**
+     * Negated !is_null() should become !== null
+     */
+    public function negatedIsNull($x): bool
+    {
+        return $x !== null;
+    }
+
+    /**
+     * Leading comparison: true === is_null($x) should simplify
+     */
+    public function leadingComparisonTrue($x): bool
+    {
+        return $x === null;
+    }
+
+    /**
+     * Leading comparison: false === is_null($x) should simplify and negate
+     */
+    public function leadingComparisonFalse($x): bool
+    {
+        return $x !== null;
+    }
+
+    /**
+     * Trailing comparison: is_null($x) === true should simplify
+     */
+    public function trailingComparisonTrue($x): bool
+    {
+        return $x === null;
+    }
+
+    /**
+     * Trailing comparison: is_null($x) === false should simplify and negate
+     */
+    public function trailingComparisonFalse($x): bool
+    {
+        return $x !== null;
+    }
+
+    /**
+     * Trailing comparison with !== true should simplify and negate
+     */
+    public function trailingComparisonNotTrue($x): bool
+    {
+        return $x !== null;
+    }
+
+    /**
+     * Trailing comparison with !== false should simplify (double negation)
+     */
+    public function trailingComparisonNotFalse($x): bool
+    {
+        return $x === null;
+    }
+}
diff --git a/tests/_data/NoIsNull/before.php b/tests/_data/NoIsNull/before.php
new file mode 100644
index 0000000..9ff4fc6
--- /dev/null
+++ b/tests/_data/NoIsNull/before.php
@@ -0,0 +1,70 @@
+<?php declare(strict_types = 1);
+
+namespace PhpCollective;
+
+class FixMe
+{
+    /**
+     * Basic is_null() should become === null
+     */
+    public function basicIsNull($x): bool
+    {
+        return is_null($x);
+    }
+
+    /**
+     * Negated !is_null() should become !== null
+     */
+    public function negatedIsNull($x): bool
+    {
+        return !is_null($x);
+    }
+
+    /**
+     * Leading comparison: true === is_null($x) should simplify
+     */
+    public function leadingComparisonTrue($x): bool
+    {
+        return true === is_null($x);
+    }
+
+    /**
+     * Leading comparison: false === is_null($x) should simplify and negate
+     */
+    public function leadingComparisonFalse($x): bool
+    {
+        return false === is_null($x);
+    }
+
+    /**
+     * Trailing comparison: is_null($x) === true should simplify
+     */
+    public function trailingComparisonTrue($x): bool
+    {
+        return is_null($x) === true;
+    }
+
+    /**
+     * Trailing comparison: is_null($x) === false should simplify and negate
+     */
+    public function trailingComparisonFalse($x): bool
+    {
+        return is_null($x) === false;
+    }
+
+    /**
+     * Trailing comparison with !== true should simplify and negate
+     */
+    public function trailingComparisonNotTrue($x): bool
+    {
+        return is_null($x) !== true;
+    }
+
+    /**
+     * Trailing comparison with !== false should simplify (double negation)
+     */
+    public function trailingComparisonNotFalse($x): bool
+    {
+        return is_null($x) !== false;
+    }
+}