JAVA-2174: Metadata.needsQuote should accept empty strings (#1204)

changelog/README.md

@@ -18,6 +18,7 @@
 - [improvement] JAVA-1950: Log server side warnings returned from a query.
 - [improvement] JAVA-2123: Allow to use QueryBuilder for building queries against Materialized Views.
 - [bug] JAVA-2082: Avoid race condition during cluster close and schema refresh.
+- [bug] JAVA-2174: Metadata.needsQuote should accept empty strings.
 
 
 ### 3.6.0

driver-core/src/main/java/com/datastax/driver/core/Metadata.java

@@ -241,11 +241,16 @@ public static String quoteIfNecessary(String id) {
   /**
    * We don't need to escape an identifier if it matches non-quoted CQL3 ids ([a-z][a-z0-9_]*), and
    * if it's not a CQL reserved keyword.
+   *
+   * <p>When 'Migrating from compact storage' after DROP COMPACT STORAGE on the table, it can have a
+   * column with an empty name. (See JAVA-2174 for the reference) For that case, we need to escape
+   * empty column name.
    */
   private static boolean needsQuote(String s) {
     // this method should only be called for C*-provided identifiers,
-    // so we expect it to be non-null and non-empty.
-    assert s != null && !s.isEmpty();
+    // so we expect it to be non-null
+    assert s != null;
+    if (s.isEmpty()) return true;
     char c = s.charAt(0);
     if (!(c >= 97 && c <= 122)) // a-z
     return true;

driver-core/src/test/java/com/datastax/driver/core/MetadataTest.java

@@ -170,6 +170,12 @@ public void escapeId_should_quote_reserved_cql_keywords() {
     assertThat(Metadata.quoteIfNecessary("columnfamily")).isEqualTo("\"columnfamily\"");
   }
 
+  /** @jira_ticket JAVA-2174 */
+  @Test(groups = "unit")
+  public void escapeId_should_quote_empty_keyword() {
+    assertThat(Metadata.quoteIfNecessary("")).isEqualTo("\"\"");
+  }
+
   @Test(groups = "unit")
   public void should_detect_reserved_keywords_in_upper_case() {
     assertThat(Metadata.isReservedCqlKeyword("COLUMNFAMILY")).isTrue();