Remove unnecessary if statement

src/main/java/org/mybatis/dynamic/sql/SqlBuilder.java

@@ -329,11 +329,11 @@ static Upper upper(BindableColumn<String> column) {
 
     // conditions for all data types
     static Exists exists(Buildable<SelectModel> selectModelBuilder) {
-        return new Exists.Builder().withSelectModelBuilder(selectModelBuilder).build();
+        return Exists.exists().withSelectModelBuilder(selectModelBuilder).build();
     }
 
     static Exists notExists(Buildable<SelectModel> selectModelBuilder) {
-        return new Exists.Builder().withSelectModelBuilder(selectModelBuilder).isNotExists().build();
+        return Exists.notExists().withSelectModelBuilder(selectModelBuilder).build();
     }
 
     static <T> IsNull<T> isNull() {

src/main/java/org/mybatis/dynamic/sql/SqlCriterionVisitor.java

@@ -3,5 +3,5 @@
 public interface SqlCriterionVisitor<R> {
     <T> R visit(ColumnAndConditionCriterion<T> criterion);
 
-    R visit(ExistsCriterion existsCriterion);
+    R visit(ExistsCriterion criterion);
 }

src/main/java/org/mybatis/dynamic/sql/where/condition/Exists.java

@@ -7,32 +7,40 @@
 
 public class Exists {
     private final Buildable<SelectModel> selectModelBuilder;
-    private final boolean isNotExists;
+    private final String operator;
 
     private Exists(Builder builder) {
         this.selectModelBuilder = Objects.requireNonNull(builder.selectModelBuilder);
-        this.isNotExists = builder.isNotExists;
+        this.operator = builder.operator;
     }
 
-    public boolean isNotExists() {
-        return isNotExists;
+    public String operator() {
+        return operator;
     }
 
     public Buildable<SelectModel> selectModelBuilder() {
         return selectModelBuilder;
     }
 
+    public static Builder exists() {
+        return new Builder();
+    }
+
+    public static Builder notExists() {
+        return new Builder().notExists();
+    }
+
     public static class Builder {
         private Buildable<SelectModel> selectModelBuilder;
-        private boolean isNotExists;
+        private String operator = "exists"; //$NON-NLS-1$
 
         public Builder withSelectModelBuilder(Buildable<SelectModel> selectModelBuilder) {
             this.selectModelBuilder = selectModelBuilder;
             return this;
         }
 
-        public Builder isNotExists() {
-            isNotExists = true;
+        private Builder notExists() {
+            operator = "not exists"; //$NON-NLS-1$
             return this;
         }
 

src/main/java/org/mybatis/dynamic/sql/where/render/CriterionRenderer.java

@@ -84,13 +84,11 @@ public Optional<RenderedCriterion> visit(ExistsCriterion criterion) {
                 .build()
                 .render();
 
-        String prefix = "exists ("; //$NON-NLS-1$
-        if (exists.isNotExists()) {
-            prefix = "not " + prefix; //$NON-NLS-1$
-        }
+        String fragment = exists.operator() + " (" //$NON-NLS-1$
+                + selectStatement.getSelectStatement() + ")"; //$NON-NLS-1$
 
         FragmentAndParameters initialCondition = FragmentAndParameters
-                .withFragment(prefix + selectStatement.getSelectStatement() + ")") //$NON-NLS-1$
+                .withFragment(fragment)
                 .withParameters(selectStatement.getParameters())
                 .build();