Cannot use, in a subwiki, a skin based on Flamingo stored in the main wiki

Caused by: org.apache.velocity.exception.MethodInvocationException: Invocation of method 'getColorThemeFromSkinFile' in  class org.xwiki.lesscss.LessCompilerScriptService threw exception java.lang.NullPointerException at <unknown template>[line 105, column 38]
	at org.apache.velocity.runtime.parser.node.ASTMethod.handleInvocationException(ASTMethod.java:243) [velocity-1.7.jar:1.7]
	at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:187) [velocity-1.7.jar:1.7]
	at org.apache.velocity.runtime.parser.node.ASTReference.execute(ASTReference.java:280) [velocity-1.7.jar:1.7]
	at org.apache.velocity.runtime.parser.node.ASTReference.value(ASTReference.java:567) [velocity-1.7.jar:1.7]
	at org.apache.velocity.runtime.parser.node.ASTExpression.value(ASTExpression.java:71) ~[velocity-1.7.jar:1.7]
	at org.apache.velocity.runtime.parser.node.ASTSetDirective.render(ASTSetDirective.java:142) ~[velocity-1.7.jar:1.7]
	at org.apache.velocity.runtime.parser.node.ASTBlock.render(ASTBlock.java:72) [velocity-1.7.jar:1.7]
	at org.apache.velocity.runtime.parser.node.ASTIfStatement.render(ASTIfStatement.java:87) ~[velocity-1.7.jar:1.7]
	at org.apache.velocity.runtime.parser.node.SimpleNode.render(SimpleNode.java:342) [velocity-1.7.jar:1.7]
	at org.xwiki.velocity.internal.DefaultVelocityEngine.evaluate(DefaultVelocityEngine.java:233) [xwiki-commons-velocity-6.3-SNAPSHOT.jar:na]
	... 71 common frames omitted
Caused by: java.lang.NullPointerException: null
	at java.io.File.<init>(File.java:277) ~[na:1.7.0_72]
	at org.xwiki.lesscss.internal.DefaultLESSSkinFileCompiler.compile(DefaultLESSSkinFileCompiler.java:91) ~[xwiki-platform-lesscss-default-6.3-SNAPSHOT.jar:na]
	at org.xwiki.lesscss.internal.DefaultLESSSkinFileCompiler.compile(DefaultLESSSkinFileCompiler.java:58) ~[xwiki-platform-lesscss-default-6.3-SNAPSHOT.jar:na]
	at org.xwiki.lesscss.internal.AbstractCachedCompiler.compileFromSkinFile(AbstractCachedCompiler.java:120) ~[xwiki-platform-lesscss-default-6.3-SNAPSHOT.jar:na]
	at org.xwiki.lesscss.internal.DefaultLESSSkinFileCompiler.compileSkinFile(DefaultLESSSkinFileCompiler.java:140) ~[xwiki-platform-lesscss-default-6.3-SNAPSHOT.jar:na]
	at org.xwiki.lesscss.internal.DefaultLESSColorThemeConverter.compile(DefaultLESSColorThemeConverter.java:94) ~[xwiki-platform-lesscss-default-6.3-SNAPSHOT.jar:na]
	at org.xwiki.lesscss.internal.DefaultLESSColorThemeConverter.compile(DefaultLESSColorThemeConverter.java:42) ~[xwiki-platform-lesscss-default-6.3-SNAPSHOT.jar:na]
	at org.xwiki.lesscss.internal.AbstractCachedCompiler.compileFromSkinFile(AbstractCachedCompiler.java:120) ~[xwiki-platform-lesscss-default-6.3-SNAPSHOT.jar:na]
	at org.xwiki.lesscss.internal.AbstractCachedCompiler.compileFromSkinFile(AbstractCachedCompiler.java:76) ~[xwiki-platform-lesscss-default-6.3-SNAPSHOT.jar:na]
	at org.xwiki.lesscss.internal.DefaultLESSColorThemeConverter.getColorThemeFromSkinFile(DefaultLESSColorThemeConverter.java:63) ~[xwiki-platform-lesscss-default-6.3-SNAPSHOT.jar:na]
	at org.xwiki.lesscss.LessCompilerScriptService.getColorThemeFromSkinFile(LessCompilerScriptService.java:133) ~[xwiki-platform-lesscss-script-6.3-SNAPSHOT.jar:na]
	at sun.reflect.GeneratedMethodAccessor250.invoke(Unknown Source) ~[na:na]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.7.0_72]
	at java.lang.reflect.Method.invoke(Method.java:606) ~[na:1.7.0_72]
	at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.doInvoke(UberspectImpl.java:395) [velocity-1.7.jar:1.7]
	at org.apache.velocity.util.introspection.UberspectImpl$VelMethodImpl.invoke(UberspectImpl.java:384) [velocity-1.7.jar:1.7]
	at org.apache.velocity.runtime.parser.node.ASTMethod.execute(ASTMethod.java:173) [velocity-1.7.jar:1.7]
	... 79 common frames omitted