Fix empty @Covers annotation causing a crash.

Author: mad-briller

src/Rules/PHPUnit/CoversHelper.php

@@ -95,6 +95,12 @@ public function processCovers(
 				))->build();
 			}
 		} else {
+			if ($covers === '') {
+				$errors[] = RuleErrorBuilder::message('@covers value does not specify anything.')->build();
+
+				return $errors;
+			}
+
 			if (!isset($method) && $this->reflectionProvider->hasFunction(new Name($covers, []), null)) {
 				return $errors;
 			}

tests/Rules/PHPUnit/ClassCoversExistsRuleTest.php

@@ -36,6 +36,10 @@ public function testRule(): void
 				'@covers value \Not\A\Class references an invalid class or function.',
 				31,
 			],
+			[
+				'@covers value does not specify anything.',
+				43,
+			],
 		]);
 	}
 

tests/Rules/PHPUnit/data/class-coverage.php

@@ -36,3 +36,10 @@ function testable(): void
 {
 
 }
+
+/**
+ * @covers
+ */
+class CoversNothing extends \PHPUnit\Framework\TestCase
+{
+}