Various Refactorings

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

@@ -46,7 +46,7 @@ private SqlColumn(Builder<T> builder) {
         alias = builder.alias;
         typeHandler = builder.typeHandler;
         renderingStrategy = builder.renderingStrategy;
-        parameterTypeConverter = builder.parameterTypeConverter;
+        parameterTypeConverter = Objects.requireNonNull(builder.parameterTypeConverter);
         tableQualifier = builder.tableQualifier;
         javaType = builder.javaType;
     }
@@ -81,7 +81,7 @@ public Optional<Class<T>> javaType() {
 
     @Override
     public Object convertParameterType(T value) {
-        return parameterTypeConverter == null ? value : parameterTypeConverter.convert(value);
+        return parameterTypeConverter.convert(value);
     }
 
     @Override
@@ -110,7 +110,7 @@ public SqlColumn<T> qualifiedWith(String tableQualifier) {
     }
 
     /**
-     * Set an alias with a camel cased string based on the column name. The can be useful for queries using
+     * Set an alias with a camel cased string based on the column name. This can be useful for queries using
      * the {@link org.mybatis.dynamic.sql.util.mybatis3.CommonSelectMapper} where the columns are placed into
      * a map based on the column name returned from the database.
      *
@@ -218,7 +218,7 @@ public static class Builder<T> {
         protected String alias;
         protected String typeHandler;
         protected RenderingStrategy renderingStrategy;
-        protected ParameterTypeConverter<T, ?> parameterTypeConverter;
+        protected ParameterTypeConverter<T, ?> parameterTypeConverter = v -> v;
         protected String tableQualifier;
         protected Class<T> javaType;
 

src/main/java/org/mybatis/dynamic/sql/common/AbstractBooleanExpressionDSL.java

@@ -28,8 +28,7 @@
 import org.mybatis.dynamic.sql.ExistsPredicate;
 import org.mybatis.dynamic.sql.SqlCriterion;
 import org.mybatis.dynamic.sql.VisitableCondition;
-import org.mybatis.dynamic.sql.exception.InvalidSqlException;
-import org.mybatis.dynamic.sql.util.Messages;
+import org.mybatis.dynamic.sql.util.Validator;
 
 public abstract class AbstractBooleanExpressionDSL<T extends AbstractBooleanExpressionDSL<T>> {
     private SqlCriterion initialCriterion; // WARNING - may be null!
@@ -146,10 +145,7 @@ private void addSubCriteria(String connector, List<AndOrCriteriaGroup> criteria)
     }
 
     protected void setInitialCriterion(SqlCriterion initialCriterion, StatementType statementType) {
-        if (this.initialCriterion != null) {
-            throw new InvalidSqlException(Messages.getString(statementType.messageNumber())); //$NON-NLS-1$
-        }
-
+        Validator.assertTrue(this.initialCriterion == null, statementType.messageNumber());
         this.initialCriterion = initialCriterion;
     }
 

src/main/java/org/mybatis/dynamic/sql/common/OrderByModel.java

@@ -23,17 +23,14 @@
 import java.util.stream.Stream;
 
 import org.mybatis.dynamic.sql.SortSpecification;
-import org.mybatis.dynamic.sql.exception.InvalidSqlException;
-import org.mybatis.dynamic.sql.util.Messages;
+import org.mybatis.dynamic.sql.util.Validator;
 
 public class OrderByModel {
     private final List<SortSpecification> columns = new ArrayList<>();
 
     private OrderByModel(Collection<? extends SortSpecification> columns) {
         Objects.requireNonNull(columns);
-        if (columns.isEmpty()) {
-            throw new InvalidSqlException(Messages.getString("ERROR.12")); //$NON-NLS-1$
-        }
+        Validator.assertNotEmpty(columns, "ERROR.12"); //$NON-NLS-1$
         this.columns.addAll(columns);
     }
 

src/main/java/org/mybatis/dynamic/sql/delete/DeleteDSL.java

@@ -78,15 +78,14 @@ public DeleteDSL<R> orderBy(Collection<? extends SortSpecification> columns) {
     @NotNull
     @Override
     public R build() {
-        DeleteModel.Builder deleteModelBuilder = DeleteModel.withTable(table)
+        DeleteModel deleteModel = DeleteModel.withTable(table)
                 .withTableAlias(tableAlias)
                 .withLimit(limit)
-                .withOrderByModel(orderByModel);
-        if (whereBuilder != null) {
-            deleteModelBuilder.withWhereModel(whereBuilder.buildWhereModel());
-        }
+                .withOrderByModel(orderByModel)
+                .withWhereModel(whereBuilder == null ? null : whereBuilder.buildWhereModel())
+                .build();
 
-        return adapterFunction.apply(deleteModelBuilder.build());
+        return adapterFunction.apply(deleteModel);
     }
 
     @Override

src/main/java/org/mybatis/dynamic/sql/insert/BatchInsertModel.java

@@ -18,22 +18,17 @@
 import java.util.Collection;
 
 import org.jetbrains.annotations.NotNull;
-import org.mybatis.dynamic.sql.exception.InvalidSqlException;
 import org.mybatis.dynamic.sql.insert.render.BatchInsert;
 import org.mybatis.dynamic.sql.insert.render.BatchInsertRenderer;
 import org.mybatis.dynamic.sql.render.RenderingStrategy;
-import org.mybatis.dynamic.sql.util.Messages;
+import org.mybatis.dynamic.sql.util.Validator;
 
 public class BatchInsertModel<T> extends AbstractMultiRowInsertModel<T> {
 
     private BatchInsertModel(Builder<T> builder) {
         super(builder);
-        if (records().isEmpty()) {
-            throw new InvalidSqlException(Messages.getString("ERROR.19")); //$NON-NLS-1$
-        }
-        if (columnMappings.isEmpty()) {
-            throw new InvalidSqlException(Messages.getString("ERROR.5")); //$NON-NLS-1$
-        }
+        Validator.assertNotEmpty(records(), "ERROR.19"); //$NON-NLS-1$
+        Validator.assertNotEmpty(columnMappings, "ERROR.5"); //$NON-NLS-1$
     }
 
     @NotNull

src/main/java/org/mybatis/dynamic/sql/insert/GeneralInsertModel.java

@@ -23,12 +23,11 @@
 
 import org.jetbrains.annotations.NotNull;
 import org.mybatis.dynamic.sql.SqlTable;
-import org.mybatis.dynamic.sql.exception.InvalidSqlException;
 import org.mybatis.dynamic.sql.insert.render.GeneralInsertRenderer;
 import org.mybatis.dynamic.sql.insert.render.GeneralInsertStatementProvider;
 import org.mybatis.dynamic.sql.render.RenderingStrategy;
 import org.mybatis.dynamic.sql.util.AbstractColumnMapping;
-import org.mybatis.dynamic.sql.util.Messages;
+import org.mybatis.dynamic.sql.util.Validator;
 
 public class GeneralInsertModel {
 
@@ -37,9 +36,7 @@ public class GeneralInsertModel {
 
     private GeneralInsertModel(Builder builder) {
         table = Objects.requireNonNull(builder.table);
-        if (builder.insertMappings.isEmpty()) {
-            throw new InvalidSqlException(Messages.getString("ERROR.6")); //$NON-NLS-1$
-        }
+        Validator.assertNotEmpty(builder.insertMappings, "ERROR.6"); //$NON-NLS-1$
         insertMappings = builder.insertMappings;
     }
 

src/main/java/org/mybatis/dynamic/sql/insert/InsertColumnListModel.java

@@ -22,18 +22,14 @@
 import java.util.stream.Stream;
 
 import org.mybatis.dynamic.sql.SqlColumn;
-import org.mybatis.dynamic.sql.exception.InvalidSqlException;
-import org.mybatis.dynamic.sql.util.Messages;
+import org.mybatis.dynamic.sql.util.Validator;
 
 public class InsertColumnListModel {
     private final List<SqlColumn<?>> columns = new ArrayList<>();
 
     private InsertColumnListModel(List<SqlColumn<?>> columns) {
         Objects.requireNonNull(columns);
-        if (columns.isEmpty()) {
-            throw new InvalidSqlException(Messages.getString("ERROR.4")); //$NON-NLS-1$
-        }
-
+        Validator.assertNotEmpty(columns, "ERROR.4"); //$NON-NLS-1$
         this.columns.addAll(columns);
     }
 

src/main/java/org/mybatis/dynamic/sql/insert/InsertModel.java

@@ -23,12 +23,11 @@
 
 import org.jetbrains.annotations.NotNull;
 import org.mybatis.dynamic.sql.SqlTable;
-import org.mybatis.dynamic.sql.exception.InvalidSqlException;
 import org.mybatis.dynamic.sql.insert.render.InsertRenderer;
 import org.mybatis.dynamic.sql.insert.render.InsertStatementProvider;
 import org.mybatis.dynamic.sql.render.RenderingStrategy;
 import org.mybatis.dynamic.sql.util.AbstractColumnMapping;
-import org.mybatis.dynamic.sql.util.Messages;
+import org.mybatis.dynamic.sql.util.Validator;
 
 public class InsertModel<T> {
     private final SqlTable table;
@@ -39,9 +38,7 @@ private InsertModel(Builder<T> builder) {
         table = Objects.requireNonNull(builder.table);
         row = Objects.requireNonNull(builder.row);
         columnMappings = Objects.requireNonNull(builder.columnMappings);
-        if (columnMappings.isEmpty()) {
-            throw new InvalidSqlException(Messages.getString("ERROR.7")); //$NON-NLS-1$
-        }
+        Validator.assertNotEmpty(columnMappings, "ERROR.7"); //$NON-NLS-1$
     }
 
     public <R> Stream<R> mapColumnMappings(Function<AbstractColumnMapping, R> mapper) {

src/main/java/org/mybatis/dynamic/sql/insert/MultiRowInsertModel.java

@@ -18,22 +18,17 @@
 import java.util.Collection;
 
 import org.jetbrains.annotations.NotNull;
-import org.mybatis.dynamic.sql.exception.InvalidSqlException;
 import org.mybatis.dynamic.sql.insert.render.MultiRowInsertRenderer;
 import org.mybatis.dynamic.sql.insert.render.MultiRowInsertStatementProvider;
 import org.mybatis.dynamic.sql.render.RenderingStrategy;
-import org.mybatis.dynamic.sql.util.Messages;
+import org.mybatis.dynamic.sql.util.Validator;
 
 public class MultiRowInsertModel<T> extends AbstractMultiRowInsertModel<T> {
 
     private MultiRowInsertModel(Builder<T> builder) {
         super(builder);
-        if (records().isEmpty()) {
-            throw new InvalidSqlException(Messages.getString("ERROR.20")); //$NON-NLS-1$
-        }
-        if (columnMappings.isEmpty()) {
-            throw new InvalidSqlException(Messages.getString("ERROR.8")); //$NON-NLS-1$
-        }
+        Validator.assertNotEmpty(records(), "ERROR.20"); //$NON-NLS-1$
+        Validator.assertNotEmpty(columnMappings, "ERROR.8"); //$NON-NLS-1$
     }
 
     @NotNull

src/main/java/org/mybatis/dynamic/sql/insert/render/GeneralInsertRenderer.java

@@ -18,11 +18,10 @@
 import java.util.Objects;
 import java.util.Optional;
 
-import org.mybatis.dynamic.sql.exception.InvalidSqlException;
 import org.mybatis.dynamic.sql.insert.GeneralInsertModel;
 import org.mybatis.dynamic.sql.render.RenderingContext;
 import org.mybatis.dynamic.sql.render.RenderingStrategy;
-import org.mybatis.dynamic.sql.util.Messages;
+import org.mybatis.dynamic.sql.util.Validator;
 
 public class GeneralInsertRenderer {
 
@@ -43,9 +42,7 @@ public GeneralInsertStatementProvider render() {
                 .map(Optional::get)
                 .collect(FieldAndValueCollector.collect());
 
-        if (collector.isEmpty()) {
-            throw new InvalidSqlException(Messages.getString("ERROR.9")); //$NON-NLS-1$
-        }
+        Validator.assertFalse(collector.isEmpty(), "ERROR.9"); //$NON-NLS-1$
 
         String insertStatement = InsertRenderingUtilities.calculateInsertStatement(model.table(), collector);
 

src/main/java/org/mybatis/dynamic/sql/insert/render/InsertRenderer.java

@@ -18,10 +18,9 @@
 import java.util.Objects;
 import java.util.Optional;
 
-import org.mybatis.dynamic.sql.exception.InvalidSqlException;
 import org.mybatis.dynamic.sql.insert.InsertModel;
 import org.mybatis.dynamic.sql.render.RenderingStrategy;
-import org.mybatis.dynamic.sql.util.Messages;
+import org.mybatis.dynamic.sql.util.Validator;
 
 public class InsertRenderer<T> {
 
@@ -41,9 +40,7 @@ public InsertStatementProvider<T> render() {
                 .map(Optional::get)
                 .collect(FieldAndValueCollector.collect());
 
-        if (collector.isEmpty()) {
-            throw new InvalidSqlException(Messages.getString("ERROR.10")); //$NON-NLS-1$
-        }
+        Validator.assertFalse(collector.isEmpty(), "ERROR.10"); //$NON-NLS-1$
 
         String insertStatement = InsertRenderingUtilities.calculateInsertStatement(model.table(), collector);
 

src/main/java/org/mybatis/dynamic/sql/render/RenderingContext.java

@@ -42,11 +42,10 @@ public class RenderingContext {
     private RenderingContext(Builder builder) {
         renderingStrategy = Objects.requireNonNull(builder.renderingStrategy);
         configuredParameterName = builder.parameterName;
+        tableAliasCalculator = Objects.requireNonNull(builder.tableAliasCalculator);
 
         // reasonable defaults
         sequence = builder.sequence == null ? new AtomicInteger(1) : builder.sequence;
-        tableAliasCalculator = builder.tableAliasCalculator == null ? TableAliasCalculator.empty()
-                : builder.tableAliasCalculator;
         calculatedParameterName = builder.parameterName == null ? RenderingStrategy.DEFAULT_PARAMETER_PREFIX
                 : builder.parameterName + "." + RenderingStrategy.DEFAULT_PARAMETER_PREFIX;  //$NON-NLS-1$
     }
@@ -96,7 +95,7 @@ public String aliasedTableName(SqlTable table) {
     }
 
     /**
-     * Crete a new rendering context based on this, with the table alias calculator modified to include the
+     * Create a new rendering context based on this, with the table alias calculator modified to include the
      * specified child table alias calculator. This is used by the query expression renderer when the alias calculator
      * may change during rendering.
      *
@@ -125,7 +124,7 @@ public static Builder withRenderingStrategy(RenderingStrategy renderingStrategy)
     public static class Builder {
         private RenderingStrategy renderingStrategy;
         private AtomicInteger sequence;
-        private TableAliasCalculator tableAliasCalculator;
+        private TableAliasCalculator tableAliasCalculator = TableAliasCalculator.empty();
         private String parameterName;
 
         public Builder withRenderingStrategy(RenderingStrategy renderingStrategy) {

src/main/java/org/mybatis/dynamic/sql/select/CountDSL.java

@@ -25,6 +25,7 @@
 import org.mybatis.dynamic.sql.SqlTable;
 import org.mybatis.dynamic.sql.configuration.StatementConfiguration;
 import org.mybatis.dynamic.sql.util.Buildable;
+import org.mybatis.dynamic.sql.util.Utilities;
 import org.mybatis.dynamic.sql.where.AbstractWhereFinisher;
 import org.mybatis.dynamic.sql.where.WhereModel;
 
@@ -33,7 +34,7 @@
  * clauses, but not the other parts of a select (group by, order by, etc.) Count queries always return
  * a long. If these restrictions are not acceptable, then use the Select DSL for an unrestricted select statement.
  *
- * @param <R> the type of model built by this Builder. Typically SelectModel.
+ * @param <R> the type of model built by this Builder. Typically, SelectModel.
  *
  * @author Jeff Butler
  */
@@ -53,9 +54,7 @@ private CountDSL(BasicColumn countColumn, SqlTable table, Function<SelectModel,
 
     @Override
     public CountWhereBuilder where() {
-        if (whereBuilder == null) {
-            whereBuilder = new CountWhereBuilder();
-        }
+        whereBuilder = Utilities.buildIfNecessary(whereBuilder, CountWhereBuilder::new);
         return whereBuilder;
     }
 
@@ -72,19 +71,16 @@ public CountDSL<R> configureStatement(Consumer<StatementConfiguration> consumer)
     }
 
     private SelectModel buildModel() {
-        QueryExpressionModel.Builder b = new QueryExpressionModel.Builder()
+        QueryExpressionModel queryExpressionModel = new QueryExpressionModel.Builder()
                 .withSelectColumn(countColumn)
                 .withTable(table())
-                .withTableAliases(tableAliases());
-
-        if (whereBuilder != null) {
-            b.withWhereModel(whereBuilder.buildWhereModel());
-        }
-
-        buildJoinModel().ifPresent(b::withJoinModel);
+                .withTableAliases(tableAliases())
+                .withJoinModel(buildJoinModel().orElse(null))
+                .withWhereModel(whereBuilder == null ? null : whereBuilder.buildWhereModel())
+                .build();
 
         return new SelectModel.Builder()
-                .withQueryExpression(b.build())
+                .withQueryExpression(queryExpressionModel)
                 .build();
     }
 

src/main/java/org/mybatis/dynamic/sql/select/GroupByModel.java

@@ -23,17 +23,14 @@
 import java.util.stream.Stream;
 
 import org.mybatis.dynamic.sql.BasicColumn;
-import org.mybatis.dynamic.sql.exception.InvalidSqlException;
-import org.mybatis.dynamic.sql.util.Messages;
+import org.mybatis.dynamic.sql.util.Validator;
 
 public class GroupByModel {
     private final List<BasicColumn> columns = new ArrayList<>();
 
     private GroupByModel(Collection<? extends BasicColumn> columns) {
         Objects.requireNonNull(columns);
-        if (columns.isEmpty()) {
-            throw new InvalidSqlException(Messages.getString("ERROR.11")); //$NON-NLS-1$
-        }
+        Validator.assertNotEmpty(columns, "ERROR.11"); //$NON-NLS-1$
         this.columns.addAll(columns);
     }
 

src/main/java/org/mybatis/dynamic/sql/select/MultiSelectDSL.java

@@ -19,6 +19,7 @@
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.List;
+import java.util.Optional;
 
 import org.jetbrains.annotations.NotNull;
 import org.mybatis.dynamic.sql.SortSpecification;
@@ -78,15 +79,11 @@ public MultiSelectModel build() {
                 .withInitialSelect(initialSelect)
                 .withUnionQueries(unionQueries)
                 .withOrderByModel(orderByModel)
-                .withPagingModel(buildPagingModel())
+                .withPagingModel(buildPagingModel().orElse(null))
                 .build();
     }
 
-    private PagingModel buildPagingModel() {
-        if (limit == null && offset == null && fetchFirstRows == null) {
-            return null;
-        }
-
+    private Optional<PagingModel> buildPagingModel() {
         return new PagingModel.Builder()
                 .withLimit(limit)
                 .withOffset(offset)