protected void checkMappingFormat(String[] vars, Statement statement) throws MatParseException {
        if (vars.length != 2) {
            throw new MatParseException("Not a valid expression should be '<varName>[.<swizzling>] = " +
                    "<nameSpace>.<varName>[.<swizzling>][:Condition]'", statement);
        }
    }
Checks if once a mapping expression is split by "=" the resulting array
have 2 elements.

@param vars      the array.
@param statement the statement.
@throws MatParseException if the array isn't correct.
jme3-core/src/plugins/java/com/jme3/material/plugins/ShaderNodeLoaderDelegate.java