update checkInputColumn to print more info if needed

Author: rekhajoshm

mllib/src/main/scala/org/apache/spark/ml/util/SchemaUtils.scala

@@ -34,11 +34,14 @@ object SchemaUtils {
    * @param colName  column name
    * @param dataType  required column data type
    */
-  def checkColumnType(schema: StructType, colName: String, dataType: DataType,
+  def checkColumnType(schema: StructType,
+                      colName: String,
+                      dataType: DataType,
                       msg: String = ""): Unit = {
     val actualDataType = schema(colName).dataType
+    val message = if (msg != null && msg.trim.length > 0) " " + msg else ""
     require(actualDataType.equals(dataType),
-      s"Column $colName must be of type $dataType but was actually $actualDataType.$msg")
+      s"Column $colName must be of type $dataType but was actually $actualDataType.$message")
   }
 
   /**