Fixed rendering of NOT condition.

Closes #1945

spring-data-relational/src/main/java/org/springframework/data/relational/core/sql/render/NotConditionVisitor.java

@@ -16,7 +16,6 @@
 package org.springframework.data.relational.core.sql.render;
 
 import org.springframework.data.relational.core.sql.Condition;
-import org.springframework.data.relational.core.sql.NestedCondition;
 import org.springframework.data.relational.core.sql.Not;
 import org.springframework.data.relational.core.sql.Visitable;
 import org.springframework.lang.Nullable;
@@ -27,7 +26,7 @@ import org.springframework.lang.Nullable;
  * @author Jens Schauder
  * @since 3.1.6
  */
-class NotConditionVisitor extends TypedSubtreeVisitor<NestedCondition> {
+class NotConditionVisitor extends TypedSubtreeVisitor<Not> {
 
 	private final RenderContext context;
 	private final RenderTarget target;
@@ -63,7 +62,7 @@ class NotConditionVisitor extends TypedSubtreeVisitor<NestedCondition> {
 
 		if (conditionVisitor != null) {
 
-			target.onRendered("NOT (" + conditionVisitor.getRenderedPart() + ")");
+			target.onRendered("NOT " + conditionVisitor.getRenderedPart());
 			conditionVisitor = null;
 		}
 

spring-data-relational/src/test/java/org/springframework/data/relational/core/sql/render/SelectRendererUnitTests.java

@@ -678,6 +678,26 @@ class SelectRendererUnitTests {
 		assertThat(sql).isEqualTo("SELECT atable.* FROM atable WHERE NOT (atable.id = 1 AND atable.id = 2)");
 	}
 
+	@Test // GH-1945
+	void notOfTrue() {
+
+		Select selectFalse = Select.builder().select(Expressions.just("*")).from("test_table")
+				.where(Conditions.just("true").not()).build();
+		String renderSelectFalse = SqlRenderer.create().render(selectFalse);
+
+		assertThat(renderSelectFalse).isEqualTo("SELECT * FROM test_table WHERE NOT true");
+	}
+
+	@Test // GH-1945
+	void notOfNestedTrue() {
+
+		Select selectFalseNested = Select.builder().select(Expressions.just("*")).from("test_table")
+				.where(Conditions.nest(Conditions.just("true")).not()).build();
+		String renderSelectFalseNested = SqlRenderer.create().render(selectFalseNested);
+
+		assertThat(renderSelectFalseNested).isEqualTo("SELECT * FROM test_table WHERE NOT (true)");
+	}
+
 	@Test // GH-1651
 	void asteriskOfAliasedTableUsesAlias() {