Merge pull request #1731 from metamx/regex-extraction-npe

fix NPE with regex extraction function

processing/src/main/java/io/druid/query/extraction/RegexDimExtractionFn.java

@@ -20,6 +20,7 @@ package io.druid.query.extraction;
 import com.fasterxml.jackson.annotation.JsonCreator;
 import com.fasterxml.jackson.annotation.JsonProperty;
 import com.google.common.base.Preconditions;
+import com.google.common.base.Strings;
 import com.metamx.common.StringUtils;
 
 import java.nio.ByteBuffer;
@@ -59,8 +60,11 @@ public class RegexDimExtractionFn extends DimExtractionFn
   @Override
   public String apply(String dimValue)
   {
+    if (dimValue == null) {
+      return null;
+    }
     Matcher matcher = pattern.matcher(dimValue);
-    return matcher.find() ? matcher.group(1) : dimValue;
+    return Strings.emptyToNull(matcher.find() ? matcher.group(1) : dimValue);
   }
 
   @JsonProperty("expr")

processing/src/test/java/io/druid/query/extraction/RegexDimExtractionFnTest.java

@@ -102,6 +102,20 @@ public class RegexDimExtractionFnTest
     Assert.assertTrue(extracted.contains("c"));
   }
 
+
+  @Test
+  public void testNullAndEmpty()
+  {
+    String regex = "(.*)/.*/.*";
+    ExtractionFn extractionFn = new RegexDimExtractionFn(regex);
+    // no match, map empty input value to null
+    Assert.assertEquals(null, extractionFn.apply(""));
+    // null value, returns null
+    Assert.assertEquals(null, extractionFn.apply(null));
+    // empty match, map empty result to null
+    Assert.assertEquals(null, extractionFn.apply("/a/b"));
+  }
+
   @Test
   public void testSerde() throws Exception
   {