Anonymous inner class constructor call referencing a getter caused NPE at compile time

import java.sql.Connection
import groovy.sql.Sql

class GrailsPrecondition {

    Connection getConnection() { database?.connection?.wrappedConnection }
    /**
     * Called from the check closure. Creates a <code>Sql</code> instance from the current connection.
     *
     * @return the sql instance
     */
    Sql getSql() {
        if (!connection) return null

        if (!sql) {
            sql = new Sql(connection) {
                protected void closeResources(Connection c) {
                    // do nothing, let Liquibase close the connection
                }
            }
        }

        sql
    }
}

java.lang.NullPointerException
	at org.codehaus.groovy.classgen.AsmClassGenerator.visitFieldExpression(AsmClassGenerator.java:1081)
	at org.codehaus.groovy.classgen.asm.ClosureWriter.loadReference(ClosureWriter.java:123)
	at org.codehaus.groovy.classgen.asm.InvocationWriter.loadVariableWithReference(InvocationWriter.java:433)
	at org.codehaus.groovy.classgen.asm.InvocationWriter.writeAICCall(InvocationWriter.java:417)
	at org.codehaus.groovy.classgen.asm.InvocationWriter.writeInvokeConstructor(InvocationWriter.java:385)
	at org.codehaus.groovy.classgen.AsmClassGenerator.visitConstructorCallExpression(AsmClassGenerator.java:914)
	at org.codehaus.groovy.ast.expr.ConstructorCallExpression.visit(ConstructorCallExpression.java:43)
	at org.codehaus.groovy.classgen.asm.BinaryExpressionHelper.evaluateEqual(BinaryExpressionHelper.java:283)
	at org.codehaus.groovy.classgen.asm.BinaryExpressionHelper.eval(BinaryExpressionHelper.java:72)
	at org.codehaus.groovy.classgen.AsmClassGenerator.visitBinaryExpression(AsmClassGenerator.java:527)
	at org.codehaus.groovy.ast.expr.BinaryExpression.visit(BinaryExpression.java:49)
	at org.codehaus.groovy.classgen.asm.StatementWriter.writeExpressionStatement(StatementWriter.java:599)
	at org.cod