Empty lines on signs rendered as "null" when upgrading 1.7.10 -> 1.8.8 -> 15w32c

tl;dr: When upgrading 1.7.10 --> 1.8.8 -->15w32c empty lines on 1.7.10 signs will be rendered as null in 15w32c.

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• World was right now created in 1.7.10
• in 1.8.8 single and double quotes were removed, empty lines of 1.7.10 remain empty but represented internally as null
• in 15w32c empty lines of the 1.7.10 signs render as null whereas the empty lines of the 1.8.8 signs remain empty
• Upgrade over 1.8.8 is necessary, when directly upgrading 1.7.10 -> 15w32c empty lines remain empty