Fixes several styling issues

Author: liancheng

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/literals.scala

@@ -41,6 +41,9 @@ object Literal {
   }
 }
 
+/**
+ * An extractor that matches non-null literal values
+ */
 object NonNullLiteral {
   def unapply(literal: Literal): Option[(Any, DataType)] = {
     Option(literal.value).map(_ => (literal.value, literal.dataType))

sql/core/src/main/scala/org/apache/spark/sql/parquet/ParquetFilters.scala

@@ -50,6 +50,8 @@ private[sql] object ParquetFilters {
         (n: String, v: Any) => FilterApi.eq(floatColumn(n), v.asInstanceOf[java.lang.Float])
       case DoubleType =>
         (n: String, v: Any) => FilterApi.eq(doubleColumn(n), v.asInstanceOf[java.lang.Double])
+
+      // Binary.fromString and Binary.fromByteArray don't accept null values
       case StringType =>
         (n: String, v: Any) => FilterApi.eq(
           binaryColumn(n),

sql/core/src/test/scala/org/apache/spark/sql/parquet/ParquetQuerySuite.scala

@@ -85,8 +85,8 @@ case class NumericData(i: Int, d: Double)
 class ParquetQuerySuite extends QueryTest with FunSuiteLike with BeforeAndAfterAll {
   TestData // Load test data tables.
 
-  var testRDD: SchemaRDD = null
-  var originalParquetFilterPushdownEnabled = TestSQLContext.parquetFilterPushDown
+  private var testRDD: SchemaRDD = null
+  private val originalParquetFilterPushdownEnabled = TestSQLContext.parquetFilterPushDown
 
   override def beforeAll() {
     ParquetTestData.writeFile()
@@ -1043,6 +1043,10 @@ class ParquetQuerySuite extends QueryTest with FunSuiteLike with BeforeAndAfterA
       Literal(null) >= 'a.int
     )
 
-    predicates.foreach(p => assert(ParquetFilters.createFilter(p).isEmpty))
+    predicates.foreach { p =>
+      assert(
+        ParquetFilters.createFilter(p).isEmpty,
+        "Comparison predicate with null shouldn't be pushed down")
+    }
   }
 }