fix: Implement missing SampleClause methods

Author: Stefan Steinhauser

src/main/java/net/sf/jsqlparser/statement/imprt/Import.java

@@ -115,4 +115,14 @@ public UnPivot getUnPivot() {
 
     @Override
     public void setUnPivot(UnPivot unpivot) {}
+
+    @Override
+    public SampleClause getSampleClause() {
+        return null;
+    }
+
+    @Override
+    public FromItem setSampleClause(SampleClause sampleClause) {
+        return null;
+    }
 }