jdk annotations for some java.sql methods, related cleanup in stdlib & tests

libraries/kotlin-jdbc/src/main/kotlin/kotlin/jdbc/Connections.kt

@@ -8,17 +8,17 @@ import java.util.Properties
 /**
  * create connection for the specified jdbc url with no credentials
  */
-fun getConnection(url : String) : Connection = DriverManager.getConnection(url)!!
+fun getConnection(url : String) : Connection = DriverManager.getConnection(url)
 
 /**
  * create connection for the specified jdbc url and properties
  */
-fun getConnection(url : String, info : Map<String, String>) : Connection = DriverManager.getConnection(url, info.toProperties())!!
+fun getConnection(url : String, info : Map<String, String>) : Connection = DriverManager.getConnection(url, info.toProperties())
 
 /**
  * create connection for the specified jdbc url and credentials
  */
-fun getConnection(url : String, user : String, password : String) : Connection = DriverManager.getConnection(url, user, password)!!
+fun getConnection(url : String, user : String, password : String) : Connection = DriverManager.getConnection(url, user, password)
 
 /**
  * Executes specified block with connection and close connection after this
@@ -65,11 +65,7 @@ fun Connection.update(template : StringTemplate) : Int {
 fun <T> Connection.query(sql: String, block: (ResultSet) -> T): T {
     return statement{
         val rs = it.executeQuery(sql)
-        if (rs != null) {
-            block(rs)
-        } else {
-            throw IllegalStateException("No ResultSet returned executeQuery($sql) on $this")
-        }
+        block(rs)
     }
 }
 
@@ -222,7 +218,7 @@ class PreparedStatementBuilder(val template : StringTemplate, val connection : C
             out.append(if (constantText) it else "?")
             constantText = !constantText
         }
-        return out.toString() ?: ""
+        return out.toString()
     }
 }
 

libraries/kotlin-jdbc/src/main/kotlin/kotlin/jdbc/PreparedStatements.kt

@@ -17,11 +17,7 @@ fun PreparedStatement.update(): Int {
 fun <T> PreparedStatement.query(block: (ResultSet) -> T): T {
     try {
         val resultSet = this.executeQuery()
-        if (resultSet == null) {
-            throw IllegalStateException("No ResultSet returned from $this")
-        } else {
-            return block(resultSet)
-        }
+        return block(resultSet)
     } finally {
         close()
     }

libraries/kotlin-jdbc/src/main/kotlin/kotlin/jdbc/ResultSets.kt

@@ -47,7 +47,7 @@ fun <T> ResultSet.map(fn : (ResultSet) -> T) : jet.Iterable<T> {
  * Returns array with column names
  */
 fun ResultSet.getColumnNames() : jet.Array<String> {
-    val meta = getMetaData()!!
+    val meta = getMetaData()
     return jet.Array<String>(meta.getColumnCount(), {meta.getColumnName(it + 1) ?: it.toString()})
 }