fixes #1566

Author: wumpz

src/main/java/net/sf/jsqlparser/expression/StringValue.java

@@ -31,7 +31,7 @@ public StringValue() {
 
     public StringValue(String escapedValue) {
         // removing "'" at the start and at the end
-        if (escapedValue.startsWith("'") && escapedValue.endsWith("'")) {
+        if (escapedValue.length() >= 2 && escapedValue.startsWith("'") && escapedValue.endsWith("'")) {
             value = escapedValue.substring(1, escapedValue.length() - 1);
             return;
         }

src/test/java/net/sf/jsqlparser/expression/StringValueTest.java

@@ -57,4 +57,10 @@ private void checkStringValue(String original, String expectedValue, String expe
         assertEquals(expectedValue, v.getValue());
         assertEquals(expectedPrefix, v.getPrefix());
     }
+    
+    @Test
+    public void testIssue1566EmptyStringValue() {
+        StringValue v = new StringValue("'");
+        assertEquals("'", v.getValue());
+    }
 }