LUCENE-5473: throw IAE not NPE when synonym map was empty

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1571986 13f79535-47bb-0310-9956-ffa450edef68

lucene/CHANGES.txt

@@ -84,6 +84,10 @@ Bug fixes
   empty list of clauses. This can happen for example,  when a wildcard matches 
   no terms.  (Tim Allison via Robert Muir)
 
+* LUCENE-5473: Throw IllegalArgumentException, not
+  NullPointerException, if the synonym map is empty when creating
+  SynonymFilter (帅广应 via Mike McCandless)
+
 Test Framework
 
 * LUCENE-5449: Rename _TestUtil and _TestHelper to remove the leading _.

lucene/analysis/common/src/java/org/apache/lucene/analysis/synonym/SynonymFilter.java

@@ -263,10 +263,10 @@ public final class SynonymFilter extends TokenFilter {
     this.synonyms = synonyms;
     this.ignoreCase = ignoreCase;
     this.fst = synonyms.fst;
-    this.fstReader = fst.getBytesReader();
     if (fst == null) {
       throw new IllegalArgumentException("fst must be non-null");
     }
+    this.fstReader = fst.getBytesReader();
 
     // Must be 1+ so that when roll buffer is at full
     // lookahead we can distinguish this full buffer from

lucene/analysis/common/src/test/org/apache/lucene/analysis/synonym/TestSynonymMapFilter.java

@@ -926,4 +926,16 @@ public class TestSynonymMapFilter extends BaseTokenStreamTestCase {
         new int[] { 8, 22, 15, 22 },
         new int[] { 1, 0, 1, 1 });
   }
+
+  public void testEmpty() throws Exception {
+    Tokenizer tokenizer = new MockTokenizer();
+    tokenizer.setReader(new StringReader("aa bb"));
+    try {
+      new SynonymFilter(tokenizer, new SynonymMap.Builder(true).build(), true);
+      fail("did not hit expected exception");
+    } catch (IllegalArgumentException iae) {
+      // expected
+      assertEquals("fst must be non-null", iae.getMessage());
+    }
+  }
 }