Fix Java9 Compiler Issue

Author: jeffgbutler

pom.xml

@@ -30,10 +30,11 @@
   <inceptionYear>2016</inceptionYear>
 
   <properties>
-    <maven.compiler.source>1.8</maven.compiler.source>
-    <maven.compiler.target>1.8</maven.compiler.target>
-    <maven.compiler.testTarget>1.8</maven.compiler.testTarget>
-    <maven.compiler.testSource>1.8</maven.compiler.testSource>
+    <java.version>8</java.version>
+    <maven.compiler.source>${java.version}</maven.compiler.source>
+    <maven.compiler.target>${java.version}</maven.compiler.target>
+    <maven.compiler.testTarget>${java.version}</maven.compiler.testTarget>
+    <maven.compiler.testSource>${java.version}</maven.compiler.testSource>
     <junit.jupiter.version>5.0.2</junit.jupiter.version>
     <junit.platform.version>1.0.2</junit.platform.version>
     <clirr.comparisonVersion>1.0.0</clirr.comparisonVersion>

src/main/java/org/mybatis/dynamic/sql/select/function/AbstractMultipleColumnArithmeticFunction.java

@@ -42,7 +42,8 @@ protected AbstractMultipleColumnArithmeticFunction(BindableColumn<T> firstColumn
 
     @Override
     public String renderWithTableAlias(TableAliasCalculator tableAliasCalculator) {
-        return Stream.of(Stream.of(column), Stream.of(secondColumn), subsequentColumns.stream())
+        // note - the cast below is added for a type inference bug in the Java9 compiler.
+        return Stream.of(Stream.of((BasicColumn) column), Stream.of(secondColumn), subsequentColumns.stream())
                 .flatMap(Function.identity())
                 .map(column -> column.renderWithTableAlias(tableAliasCalculator))
                 .collect(Collectors.joining(padOperator(), "(", ")")); //$NON-NLS-1$ //$NON-NLS-2$