Fix RegexpMultiline causing exception with default config. #1129

config/checkstyle_checks.xml

@@ -52,9 +52,10 @@
     <property name="maximum" value="0"/>
   </module>
 
+  <module name="RegexpMultiline"/>
+
   <!-- 
   <module name="RegexpHeader"/>
-  <module name="RegexpMultiline"/>
   <module name="UniqueProperties"/>
   -->
   <module name="TreeWalker">

src/main/java/com/puppycrawl/tools/checkstyle/checks/regexp/DetectorOptions.java

@@ -35,8 +35,11 @@ class DetectorOptions {
     private final int compileFlags;
     /** Used for reporting violations. */
     private final AbstractViolationReporter reporter;
-    /** Format of the regular expression to check for. */
-    private String format;
+    /**
+     * Format of the regular expression to check for. Default value is pattern that never matches
+     * any string.
+     */
+    private String format = "$.";
     /** The message to report on detection. If blank, then use the format. */
     private String message = "";
     /** Minimum number of times regular expression should occur in a file. */

src/test/java/com/puppycrawl/tools/checkstyle/checks/regexp/RegexpMultilineCheckTest.java

@@ -112,4 +112,11 @@ public class RegexpMultilineCheckTest extends BaseFileSetCheckTestSupport {
         verify(checkConfig, file.getPath(), expected);
     }
 
+    @Test
+    public void testDefaultConfiguration() throws Exception {
+        final DefaultConfiguration checkConfig = createCheckConfig(RegexpMultilineCheck.class);
+        final String[] expected = {
+        };
+        verify(checkConfig, getPath("InputSemantic.java"), expected);
+    }
 }