[CARBONDATA-3344] Fix Drop column not present in table

Why this PR needed?
When trying to drop column which is not present in main table, it is throwing Null pointer exception, instead of throwing exception for column does not exists in table.

This closes #3174

integration/spark-common-cluster-test/src/test/scala/org/apache/carbondata/cluster/sdv/generated/AlterTableTestCase.scala

@@ -29,6 +29,8 @@ import org.apache.carbondata.core.constants.CarbonCommonConstants
 import org.apache.carbondata.core.util.CarbonProperties
 import org.apache.spark.sql.catalyst.analysis.NoSuchTableException
 
+import org.apache.carbondata.spark.exception.ProcessMetaDataException
+
 /**
  * Test Class for AlterTableTestCase to verify all scenerios
  */
@@ -1024,6 +1026,16 @@ class AlterTableTestCase extends QueryTest with BeforeAndAfterAll {
     }
   }
 
+  test("Test drop columns not present in the table") {
+    sql("drop table if exists test1")
+    sql("create table test1(col1 int) stored by 'carbondata'")
+    val exception = intercept[ProcessMetaDataException] {
+      sql("alter table test1 drop columns(name)")
+    }
+    assert(exception.getMessage.contains("Column name does not exists in the table default.test1"))
+    sql("drop table if exists test1")
+  }
+
   val prop = CarbonProperties.getInstance()
   val p1 = prop.getProperty("carbon.horizontal.compaction.enable", CarbonCommonConstants.CARBON_HORIZONTAL_COMPACTION_ENABLE_DEFAULT)
   val p2 = prop.getProperty("carbon.horizontal.update.compaction.threshold", CarbonCommonConstants.DEFAULT_UPDATE_DELTAFILE_COUNT_THRESHOLD_IUD_COMPACTION)

integration/spark2/src/main/scala/org/apache/spark/sql/execution/command/schema/CarbonAlterTableDropColumnCommand.scala

@@ -76,15 +76,6 @@ private[sql] case class CarbonAlterTableDropColumnCommand(
         }
       }
 
-      // Check if column to be dropped is of complex dataType
-      alterTableDropColumnModel.columns.foreach { column =>
-        if (carbonTable.getColumnByName(alterTableDropColumnModel.tableName, column).getDataType
-          .isComplexType) {
-          val errMsg = "Complex column cannot be dropped"
-          throw new MalformedCarbonCommandException(errMsg)
-        }
-      }
-
       val tableColumns = carbonTable.getCreateOrderColumn(tableName).asScala
       var dictionaryColumns = Seq[org.apache.carbondata.core.metadata.schema.table.column
       .ColumnSchema]()
@@ -99,6 +90,11 @@ private[sql] case class CarbonAlterTableDropColumnCommand(
                 dictionaryColumns ++= Seq(tableColumn.getColumnSchema)
               }
             }
+            // Check if column to be dropped is of complex dataType
+            if (tableColumn.getDataType.isComplexType) {
+              val errMsg = "Complex column cannot be dropped"
+              throw new MalformedCarbonCommandException(errMsg)
+            }
             columnExist = true
           }
         }