Align with the APIs documentation of ColumnVector's get methods

Author: cfmcgrady

common/src/main/java/org/apache/comet/vector/CometListVector.java

@@ -45,6 +45,7 @@ public CometListVector(
 
   @Override
   public ColumnarArray getArray(int i) {
+    if (isNullAt(i)) return null;
     int start = listVector.getOffsetBuffer().getInt(i * ListVector.OFFSET_WIDTH);
     int end = listVector.getOffsetBuffer().getInt((i + 1) * ListVector.OFFSET_WIDTH);
 

common/src/main/java/org/apache/comet/vector/CometMapVector.java

@@ -65,6 +65,7 @@ public CometMapVector(
 
   @Override
   public ColumnarMap getMap(int i) {
+    if (isNullAt(i)) return null;
     int start = mapVector.getOffsetBuffer().getInt(i * MapVector.OFFSET_WIDTH);
     int end = mapVector.getOffsetBuffer().getInt((i + 1) * MapVector.OFFSET_WIDTH);
 

common/src/main/java/org/apache/comet/vector/CometPlainVector.java

@@ -123,6 +123,7 @@ public double getDouble(int rowId) {
 
   @Override
   public UTF8String getUTF8String(int rowId) {
+    if (isNullAt(rowId)) return null;
     if (!isBaseFixedWidthVector) {
       BaseVariableWidthVector varWidthVector = (BaseVariableWidthVector) valueVector;
       long offsetBufferAddress = varWidthVector.getOffsetBuffer().memoryAddress();
@@ -147,9 +148,7 @@ public UTF8String getUTF8String(int rowId) {
 
   @Override
   public byte[] getBinary(int rowId) {
-    if (isNullAt(rowId)) {
-      return null;
-    }
+    if (isNullAt(rowId)) return null;
     int offset;
     int length;
     if (valueVector instanceof BaseVariableWidthVector) {

common/src/main/java/org/apache/comet/vector/CometVector.java

@@ -85,6 +85,7 @@ public boolean isFixedLength() {
 
   @Override
   public Decimal getDecimal(int i, int precision, int scale) {
+    if (isNullAt(i)) return null;
     if (!useDecimal128 && precision <= Decimal.MAX_INT_DIGITS() && type instanceof IntegerType) {
       return createDecimal(getInt(i), precision, scale);
     } else if (precision <= Decimal.MAX_LONG_DIGITS()) {