Fix Vertical aligner when rows are empty

Fixes https://github.com/spring-projects/spring-shell/issues/107

src/main/java/org/springframework/shell/table/DelimiterTextWrapper.java

@@ -46,7 +46,9 @@ public class DelimiterTextWrapper implements TextWrapper {
 				result.add(String.format("%-" + columnWidth + "s", toAdd));
 				line = line.substring(split == -1 ? columnWidth : split + 1);
 			}
-			result.add(String.format("%-" + columnWidth + "s", line)); // right pad if necessary
+			if (columnWidth > 0) {
+				result.add(String.format("%-" + columnWidth + "s", line)); // right pad if necessary
+			}
 		}
 		return result.toArray(new String[result.size()]);
 	}

src/main/java/org/springframework/shell/table/SimpleVerticalAligner.java

@@ -32,20 +32,25 @@ public enum SimpleVerticalAligner implements Aligner {
 		String[] result = new String[cellHeight];
 		int blanksBefore = 0;
 		int blanksAfter = 0;
+		boolean atLeastOneNonEmptyRow = false;
 		for (int row = 0; row < text.length; row++) {
 			if (text[row] == null || text[row].trim().equals("")) {
 				blanksBefore++;
 			}
 			else {
+				atLeastOneNonEmptyRow = true;
 				break;
 			}
 		}
-		for (int row = text.length - 1; row >= 0; row--) {
-			if (text[row] == null || text[row].trim().equals("")) {
-				blanksAfter++;
-			}
-			else {
-				break;
+		// In case of full blank, don't count blank rows twice
+		if (atLeastOneNonEmptyRow) {
+			for (int row = text.length - 1; row >= 0; row--) {
+				if (text[row] == null || text[row].trim().equals("")) {
+					blanksAfter++;
+				}
+				else {
+					break;
+				}
 			}
 		}
 		String filler = spaces(cellWidth);

src/test/java/org/springframework/shell/table/TableTest.java

@@ -90,4 +90,12 @@ public class TableTest extends AbstractTestWithSample {
 
 	}
 
-}
+	@Test
+	public void testEmptyCellsVerticalAligner() {
+		TableModel model = new ArrayTableModel(new String[][] {{"a", "b"}, {null, null}});
+		Table table = new TableBuilder(model).on(CellMatchers.table()).addAligner(SimpleVerticalAligner.middle).build();
+		String result = table.render(3);
+
+	}
+
+}